Top seed Novak Djokovic reached the French Open quarter-finals for a record-extending 11th successive year by easing through his biggest test yet in Russian 15th seed Karen Khachanov.

Djokovic will face Pablo Carreno Busta or Daniel Altmaier in the last eight.

Greek fifth seed Stefanos Tsitsipas reached his first quarter-final with victory over Bulgarian Grigor Dimitrov.

Tsitsipas will play 13th seed Andrey Rublev after the Russian's 6-7 (4-7) 7-5 6-4 7-6 (7-3) win over Marton Fucsovics.

That quarter-final will be a rematch of last month's Hamburg final, where Rublev beat Tsitsipas in three sets.

Focused Djokovic eases through first real test

Djokovic is one of the favourites to win the clay-court Grand Slam in Paris, along with 12-time champion Rafael Nadal and recent US Open winner Dominic Thiem.

While Thiem overcame a battle against young Frenchman Hugo Gaston on Sunday, the world number one joined Nadal in reaching the quarter-finals without dropping a set.

The 17-time Grand Slam champion had breezed through the opening three rounds, having lost a combined total of 15 games against Swedish youngster Mikael Ymer, Lithuania's Ricardas Berankis and Colombia's Daniel Elahi Galan.

This promised to be Djokovic's first test against a player of decent pedigree and, apart from losing a couple of breaks, he will be pleased with his intent and execution against the powerful former world number eight.

In each of his previous matches, Djokovic had asserted himself early by breaking serve and managed to do that for a 5-3 lead after the pressure finally told on Khachanov in a lengthy game.

A loud roar came from Djokovic, indicating a mixture of delight and relief, as he looked to serve out the opening set.

Khachanov had won only two points on the Serb's serve up to that point but there was an unexpected twist as he broke straight back. However, he could not maintain the pressure and lost serve as Djokovic clinched the opener.

Djokovic grew in confidence from that point, not only soaking up Khachanov's power but managing to frustrate his opponent by consistently turning defence into attack.

Another fine example of that came in the eighth game of the second set when he sent a stretching backhand flying down the line to safety for three set points. Khachanov saved all of them - and then a fourth - to eventually hold, forcing Djokovic to serve out the set.

Khachanov was producing a decent level. His problem was that it was Djokovic at the opposite side of the court.

After losing serve in the first game of the third set, the Russian fought back to 2-2 and had chances to break again for a 4-2 lead. However, Djokovic - who tried to move Khachanov forward with plenty of drop-shots - reasserted control to hold serve and then claim the next three games for victory.

Djokovic hits another line judge accidentally

Another win for Djokovic means he has still not lost a completed match this year, with his only defeat in 36 matches coming when he was defaulted from the US Open last month.

Djokovic was disqualified when he accidentally hit a line judge after swatting away a spare ball in frustration after losing serve in his fourth-round match against Carreno Busta.

This is his first Grand Slam since that controversy and there was another anxious moment for him in the first set when a Khachanov return flew off the Serb's racquet into a line judge's face.

Thankfully, the man was unhurt and there was no chance of a default as the ball was still in play and it was not a dangerous action from Djokovic.

However, it might have been a worrying reminder of what happened in New York - as could be lining up against Carreno Busta again.

First the Spanish 17th seed must beat German qualifier Altmaier, who is making his Grand Slam debut.

Disciplined Tsitsipas through after 'very responsible' win

Tsitsipas, 22, was playing former world number three Dimitrov for the first time and came through in a 6-3 7-6 (11-9) 6-2 win on Court Philippe Chatrier.

Tsitsipas raced to a 3-0 lead in the opening set and it was that early break that proved decisive despite Dimitrov's efforts to carve out three break points when the Greek was serving for the set.

But the Bulgarian failed to take his chances and then missed at crucial moments in the second, squandering two set points with a backhand into the net and a wide forehand.

He then gifted Tsitsipas the set with a forehand into the net tape when he had the whole court at his disposal while the Greek was scrambling to get back into position after retrieving a wide shot.

"The tie-break was where all the money went. I tried to take it point by point, I showed a lot of discipline. It was a very responsible win in the second set," said Tsitsipas, who had a medical timeout for an irritated left eye.

Tsitsipas, who won the ATP Finals last year, built on his momentum to break early in the third and then again in the eighth game to reach his second Grand Slam quarter-final after making the Australian Open semi-finals in 2019.

"My aggressiveness on return games and my focus on important points made the difference," Tsitsipas said.