Novak Djokovic passed his first real test at this year's French Open in style as he battled past Russia's Karen Khachanov 6-4, 6-3, 6-3 on Monday to reach the quarter-finals for the 14th time.
The 33-year-old claimed a fourth successive straight-sets victory in his latest quest for a second French Open title.
Djokovic faced stiff resistance before taking the first set and had an anxious moment when his attempted return off one Khachanov serve bounced off his frame and struck a line judge in the head, reviving memories of his U.S. Open debacle.
Khachanov saved four set points at 2-5 in the second set before Djokovic moved two sets clear.
Djokovic appeared to be in cruise control when he led 2-0 in the third but Khachanov took the next three games and had two break points for a 4-2 lead.
The Serb held, though, and regained control to ease into his 47th Grand Slam quarter-final.
Djokovic hit 44 winners and has yet to drop a set in the tournament, losing only 25 games in four rounds.
"It was a very even match, perhaps more difficult than the result showed," said Djokovic.
Meanwhile, Petra Kvitova returned to the French Open quarter-finals for the first time in eight years.
Two-time Wimbledon champion Kvitova is through to the last eight at Roland Garros for just the second time. Her best run in Paris came when she reached the semi-finals in 2012.
Seventh seed Kvitova, who missed last year's tournament due to an arm injury, defeated China's Zhang Shuai 6-2, 6-4 and will next play German veteran Laura Siegemund.
"After eight years to be in the quarter-final again, it's great. I'm really happy for that, that I'm still able to play on all surfaces," said Kvitova.
"When the roof is closed it's like being indoors and I really love to play."
Also, Stefanos Tsitsipas overcame an eye problem to become the first Greek man to reach the last eight of the French Open with a 6-3, 7-6 (11/9), 6-2 win over Grigor Dimitrov of Bulgaria.
The 22-year-old will now take on Andrey Rublev in a repeat of the recent Hamburg final which was won by the Russian.
Fifth seed Tsitsipas has won 12 successive sets at the tournament having been two sets down to Jaume Munar in the opening round.
Rublev, the 13th seed, also advanced to the quarter-finals for the first time after battling past Marton Fucsovics of Hungary 6-7 (4/7), 7-5, 6-4, 7-6 (7/3).
In a match which featured 12 breaks of serve, the 22-year-old Rublev had been a break down in the second and third sets. He also had to save three set points in the fourth.
"I knew it would be tough," said Rublev who arrived in Paris having reached his second US Open quarter-final last month.
"I had a little bit of luck today. There was a lot of wind so you are going to lose your serve a lot in those conditions."
