Silence around the stadium as Pete Sampras prepares to serve on match point at Wimbledon. It's a familiar setting for the American, a seven-time champion, but today is different.

On the other side of the net his teenage opponent waits, hair in a neat pony tail, wooden bead jewellery around his neck. It's his first appearance in front of the Centre Court crowd.

Sampras crashes a serve out wide and begins a charge towards the net, he wants to follow up with a signature volley. But the return is too powerful and beyond his reach as it comes thumping down the line. It all happens so quickly. The crowd roars as the 19-year-old winner falls to the ground in disbelief, a five-set epic over in an instant. He has beaten the champion, his idol.

"Game, set and match…

"Federer!"

On 2 July 2001, with world number one Sampras, then aged 29, expected to win a fifth straight Wimbledon title, Roger Federer claimed a stunning victory in the fourth round. It was a breakthrough moment for a young man who has gone on to usurp his hero's remarkable record at SW19.

Twenty years later, Federer is now a 20-time Grand Slam winner. He has won Wimbledon eight times - one more than Sampras. He'll play at this year's tournament just over a month before his 40th birthday.

Here, BBC Sport looks back on that Sampras-Federer match-up, the only time these two tennis greats would meet on court in an official match. It was a landmark moment in the evolution of the modern game.

The second Monday of Wimbledon is known as 'Manic Monday'. All 32 men and women remaining in the singles draws are scheduled to play on the same day and upsets are highly anticipated. Still, there were only a few who might have expected on Centre Court.

Sampras was going for a record-extending eighth title and had only lost once at the All England Club since 1993. Federer was an enigmatic talent making his way in the game. He'd won the prestigious boys' championship at Wimbledon in 1998 and was seeded 15, but for many in the crowd, he was an unknown.

Iain Carter was commentating for BBC Radio 5 Live. He'd been first alerted to Federer's vast potential at the Australian Open the previous year.

"I remember driving into Wimbledon with a real sense of excitement because already Federer had shown signs that he'd be a special talent, you knew he was going to be the next big thing," Carter says.

"You also knew that Sampras was a little bit vulnerable. He'd lost to Marat Safin in the US Open final the year before and against Todd Martin in the Australian Open fourth round. But of course he was 'Mr Invincible' on grass."

Paul Annacone, Sampras's coach, had scouted the young Swiss. He was anticipating a tough match.

"Everybody knew how talented Roger was, an incredibly gifted athlete," says Annacone, who reached a world ranking of 12 in his career.

"The question with a young player like that is how they're going to handle the big moment. That you don't know."

The answer comes early in the first set. If Federer has any nerves there are no signs of them as he carves out three break points in Sampras' second service game. The champion has to claw back control and hold on, all the way to a tie-break.

It's Sampras who reaches the first set point - hitting 121mph on his second serve to make it 6-5. He's then incensed with the line judge's call as Federer's serve is deemed in for 6-6.

The tie-break reaches 7-7 when Federer's return clips the net and Sampras has to improvise to slice his volley back over the net. Federer then blasts a backhand straight at the American, which he volleys long. It gives Federer his second set point, this time on his serve.

Sampras' backhand into the net seals a nail-biting first set for the Swiss teenager. The scene is set for a classic.

"The atmosphere grew and grew," says Carter. "There was a collective sense of hubbub, people thinking: 'Hang on, there's something happening here.' The way Federer moved so gracefully about the court was eye-catching."

Sampras' record at Wimbledon cannot be overstated. He'd won 56 of his previous 57 matches and claimed more singles titles than any other male player in the competition's history. His 13 Grand Slams was a world record in the men's game at that time.

"One of Pete's biggest strengths is that he's so pragmatic," Annacone says. "Whether it's Wimbledon, Miami, Monte Carlo or the French Open, he was methodical about his routine and this year was no different.

"He was feeling pretty comfortable, but he has that balance of having confidence without taking anything for granted."

Two double faults from Federer with the score 5-6 in the second set and Sampras takes a 0-40 lead for three set points. Federer fights back to deuce but the top seed's experience tells. There's a fist pump from Sampras as his opponent's forehand volley at the net sails long. The scores are levelled at one set each.

British number one Tim Henman and Sampras were good friends, they practised together and both played an aggressive serve-and-volley game. They'd met seven times with Sampras winning six, including the Wimbledon semi-finals of 1998 and 1999.

"His single-mindedness, and how he was able, on and off the court, to maintain this incredible focus meant he let nothing distract him in the pursuit of winning majors," says Henman.

It was quickly becoming clear that level of concentration was going to be tested to its limits by his young Swiss challenger.

Into the third set and Sampras leads 40-15 with the score level at 4-4. But Federer fights back to earn break point - the 13th of a very close match.

Sampras goes to his trademark serve and charge to the net. Federer's sliced backhand return shoots up into the air - and Sampras is ready to end the point with a smash. Federer has to guess. He goes to his right and Sampras has the court gaping. The champion chooses power but does not catch his shot and the ball flies long for Federer to break.

"If Sampras was now to lose this match, that could be the shot that costs him the title," says the late David Mercer on the BBC TV commentary.

Federer holds his serve to win the set 6-4. He leads the match again.

Thinking back to when he saw Federer play for the first time, against Andre Agassi in his home town of Basel in Switzerland, BBC commentator David Law saw similarities between him and Sampras immediately.

He says: "Federer played slightly differently and played more from the baseline than Sampras did, but the way he moved, his strokes, he was sponsored by the same company and wore the same clothes, had the same racquet sponsor, it was like they'd created this little Sampras."

Agassi would win that match comfortably, 6-3 6-2. But he told Law afterwards that he expected Federer to develop into a top player.

One challenge the Swiss regularly had to overcome in his formative years was his own temper. He has spoken countless times about his behaviour as a junior, breaking racquets and acting out on court.

Yet here he was on the biggest stage of them all, two sets to one up against possibly the greatest men's grass-court tennis player of all time, and into a fourth-set tie-break.

Sampras serves flawlessly this time, racing into a 6-2 lead. He's now serving to take the match to a deciding final set. The rapidly maturing Federer remains calm. No sign of any dip in concentration. No anger.

Federer returns another fast serve short towards the net. The onrushing American uses all his skill and experience to play a sumptuous half-volley drop shot across the court; a gut-busting sprint is not enough to get Federer there in time. This match is going the distance - we'll have a fifth, deciding set.

Though he was yet to play his last-16 match against American Todd Martin, Henman was aware of the classic that was unfolding on Centre Court. If he beat Martin, he would play the winner.

While he'd struggled in previous meetings against Sampras, he had a 100% record against Federer - two wins from two.

Henman says: "Sampras was the king of Wimbledon at that stage, and although Federer was a very good player, given the choice of who to play it would have been Federer every day of the week."

Four games all in the final set and Sampras carves out a break point at 30-40. He goes for backhand power from the baseline but doesn't quite catch his shot and Federer puts a volley away for deuce.

Advantage Sampras now and another break point. Federer's first serve catches the top of the net and lands long. Gasps in the crowd; this could be the champion's moment to strike a fatal blow.

Federer's second serve pushes the American out wide on his backhand. The Swiss meets his return moving in, with a powerful forehand to the other side of the court. Rushing across, Sampras gets there and strikes straight down the line. If it goes in he breaks, but it hits the net - deuce. Federer wins the next two points to hold his serve. The score's now 5-4.

In the players' box, Annacone is impressed by what he sees.

"I remember thinking after Pete won the fourth set, now this is crunch time, where he plays really well, so I was curious to see what Roger did," he says.

"Roger getting out of that game at 4-4, I thought: 'Wow, this kid's really good under pressure.'"

Both players hold their next service games to take the score to 6-5. Sampras is now serving to stay in the match. First serve - long. Second serve - let. Murmurs in the crowd.

Sampras sends a top-spin second serve down the middle but can do nothing as Federer's majestic backhand return powers past him. 0-15.

On the next point the first serve is in. Federer returns and Sampras attempts to cushion a volley back towards the baseline. He gets underneath the shot and sends the ball long. 0-30.

"Two points from putting out the champion," says Mercer in commentary, with the crowd noise growing.

Sampras serves down the middle and Federer can't return. 15-30. He serves out wide on to Federer's backhand and charges in, Federer's return is to his right and the champion's crosscourt volley hits the net tape. 15-40. Two match points.

Federer only needs one, his return of serve crashes down the line.

"He's done it! The champion is out!" shouts Mercer over a deafening roar. The match is over after three hours and 41 minutes. The final score: 7-6 (9-7) 5-7 6-4 6-7 (2-7) 7-5.

The young pretender soaks in the applause, arms held high with a look of disbelief before taking his seat. He's overcome by the emotion. It's his greatest accomplishment to date.

Federer waits for his opponent to leave the court to a standing ovation and follows close behind. Having never played on Wimbledon's premier show court, he needs a prompt from the seasoned champion to bow towards the Royal Box as they exit.

"This match will give me as much confidence as I can get," Federer says. "This is the biggest win of my life."

Sampras adds: "There are a lot of young guys coming up but Roger is a bit extra special."

Annacone, who would later coach Federer, saw the match as a "passing of the torch" in the men's game.

"It was two of the best athletes of their time and the beginning of Roger Federer," he adds.

Federer would go on to lose to Henman in the quarter-final in four sets, with the Briton himself beaten by eventual winner Goran Ivanisevic over a rain-soaked three days in the semi-finals.

Two years later the Swiss won his first Wimbledon title, beating Australian Mark Philippoussis in the final. It began a period of incredible dominance that included 12 Grand Slam titles in just over four years - and five men's singles titles in a row at both Wimbledon and the US Open.

Sampras would add one more Grand Slam with the 2002 US Open, which took his total to a men's record 14. He never played professionally again and announced his retirement the following year.

Annacone says: "I remember when he told me. He said: 'I was playing to win another major and I was playing to prove myself to myself. I don't need to do that any more. I'm done, I'm happy.'

"And that was it, he stopped. That's Pete's personality."

Federer, having lost to Rafael Nadal in the 2008 Wimbledon final in what many believe to be the greatest match of all time, added the 2008 US Open and his only French Open title to date in 2009 to equal Sampras' Grand Slam record of 14 titles.

And later that year, Sampras returned to Centre Court to watch Federer beat Andy Roddick and claim his 15th.

"I want to be there when Federer breaks my record. I want to see it, I want to feel it," he told Law in an interview the year before. Respect between the two great champions was mutual.

Federer would go on to claim his eighth Wimbledon title in 2017, breaking another of Sampras' records.

His jaw-dropping dominance, and the emergence of Nadal and Novak Djokovic, has seen 59 Grand Slams shared between the three great rivals (Federer 20, Nadal 20, Djokovic 19).

"To me, that's what's so remarkable - that the three of them have gone way past Sampras' 14 majors," says Henman.

"That's 14 and a half years of slams just being won by those three. It is absolutely incredible."

Federer goes into this year's Wimbledon championships a few weeks before his 40th birthday.

Law first met him when he was 16 years old, shortly after his triumph at Wimbledon as a junior. He was tasked with gathering some basic information for a player bio. The 16-year-old with short, curly hair told him he liked computer games and his tennis idols were Stefan Edberg, Boris Becker and Sampras.

He's seen little change in his persona, despite all the success.

"He walks the Earth very lightly and loves everything about what he is," says Law.

"I get the feeling he can't believe his luck and it makes him very easy to be around. He's still as wide-eyed and excited by it as he was then. He's not worn down by anything, it's all still new and fun to him and that's great to see."

The rivalry between Federer, Nadal and Djokovic has captivated the sporting world for more than a decade, yet that day in 2001 would be the only time Wimbledon's greatest men's champions went head-to-head.

"Those of us who were lucky enough to be there witnessed a unique moment," says Carter.

"From one glorious champion to another, it was a change of era in tennis and a lift-off moment for the game. You can draw it all the way back to that single match.

"And I think for something as glorious as we've seen in these last two decades, to have a single spark for it is totally appropriate."