Nick Kyrgios will face top seed Rafael Nadal in the last 16 at the Australian Open after an "insane" five-set win over Karen Khachanov.

Kyrgios, who missed match points in the third and fourth sets, won 6-2 7-6 (7-5) 6-7 (6-8) 6-7 (7-9) 7-6 (10-8).

The Australian, 24, needed nearly four-and-a-half hours to win a tense third-round match against the Russian - having led by two sets and a break.

But he came through in a final-set tie-break at a boisterous Melbourne Arena.

"It was definitely one of the craziest matches I've ever been a part of," Kyrgios said.

Kyrgios leads 2-1 in his head-to-head record on hard courts against Nadal, with whom he has rarely seen eye-to-eye, although the 19-time Grand Slam champion leads 4-3 on all surfaces.

The pair, who will meet at Melbourne Park on Monday, last faced each other on grass at Wimbledon in July when Nadal won in four sets.

The Spanish top seed, 33, cruised past compatriot Pablo Carreno Busta 6-1 6-2 6-4 in his third-round match earlier on Saturday.

The world number one wrapped up a straightforward win almost seven hours earlier than Kyrgios, whose brutal contest against Khachanov lasted for four hours and 26 minutes.

"I'm not thinking about that [playing Nadal] - I'm just thinking about my legs and getting them into an ice bath," Kyrgios said.

Kyrgios fights way into last 16

The prospect of another meeting between Kyrgios and Nadal has been a tantalising one since the Australian Open draw was made nine days ago.

Kyrgios has previously described Nadal as "super salty", while Nadal has been visibly irritated by the Australian's erratic on-court behaviour in the past.

To add further spice to a highly-anticipated blockbuster, Kyrgios cheekily mocked Nadal's superstitious service routine in his second-round win over France's Gilles Simon.

And, after Nadal thrashed Carreno Busta in his "best match of the tournament", Kyrgios ensured it would happen by seeing off 16th seed Khachanov.

"Whatever happens between us, he [Nadal] is an amazing player. Arguably the greatest of all time," Kyrgios said.

"At the end of the day, we're two different tennis players. We go about it completely different."

After clinching victory over Khachanov, Kyrgios fell to the court in celebration and laid out on the baseline before rising to wearily take the acclaim of the crowd.

Few would have predicted the drama which followed after Kyrgios, with his generally more relaxed demeanour, bettered Khachanov in all the key areas during the first two sets.

Kyrgios had a higher first-serve percentage, won more first-serve points, hit more aces and cracked more winners, while throwing in several drop-shots to unsettle the Russian.

Khachanov's frustration at being outplayed - and some calling out from the crowd during play - was laid bare when he whacked a loose ball into the court's roof during the third set.

That anger seemed to spur him into finding a different level, clawing a set back when Kyrgios hit a wild forehand wide and then levelling after a fourth set where he made just two unforced errors.

Kyrgios led 3-0 in the deciding first-to-10 tie-break, used to settle matches that reach 6-6 in the fifth set at the Australian Open.

Roars greeted every winning point for the Australian number two, with anguished cries heard as Khachanov fought back in a gripping battle.

The pair were deadlocked at 6-6, then 7-7, before a Kyrgios forehand into the net post gave Khachanov an opportunity to serve out the match.

However, a pinpoint backhand down the line finished a tense rally, leaving Kyrgios grinning and the crowd on their feet as Khachanov missed his chance.

Khachanov then hit a backhand into the net for Kyrgios' third match point - one hour and 54 minutes after his first - and pushed another wide to cause pandemonium in the Melbourne Arena.

Kyrgios described the match as "insane" as he struggled to speak on court afterwards.

"At 8-7 down, I had all the thoughts. I thought I was going to lose. I was thinking about everything. I was thinking about the media if I lost, everything," he added.

Up next, the world number one

Nadal, 33, was sharp on serve as he raced into a two-set lead in his match, allowing 27th seed Carreno Busta just five return points.

Carreno Busta fared little better in the third as 2009 champion Nadal wrapped up a one-sided win over his friend, with whom he helped Spain win the Davis Cup in November in one hour and 38 minutes.

Nadal set the tone by breaking in the second game of the match, pinching Carreno Busta's serve another four times on a sun-soaked Rod Laver Arena.

"It was my best match of the tournament without a doubt," said Nadal, who hit 42 winners and made just seven unforced errors.

"When the conditions are warmer, the ball bounces higher and flies through the air. That helps my game.

"I did very well with my serves and started to hit some forehands down the line. That is key for me."

Victory also continued Nadal's dominance over his compatriots. The Majorcan left-hander has now won his past 18 matches against Spanish opposition, stretching back to a 2016 Australian Open first-round defeat by Fernando Verdasco.