Novak Djokovic looked to be heading for a shock French Open defeat on Monday before the world No 1 fought back to secure victory against teenager Lorenzo Musetti.
The Serbian looked out of sorts against world No 76 Musetti, who was playing his first Grand Slam main draw, and lost the opening two sets on tiebreaks.
But Musetti's batteries seemed to drain away from that point as Djokovic won the next two sets convincingly before the Italian retired with an injury in the fifth, with the scores at 6-7, 6-7, 6-1, 6-0, 4-0.
It was the fifth time in his Grand Slam career that the 34-year-old has come back from two sets down to win.
Djokovic, the 2016 champion who is chasing a 19th major, won 53 of the last 61 points against Musetti as he made a quarter-final at the majors for the 49th time.
The win set up a last-eight clash with Matteo Berrettini, another Italian, who progressed after Roger Federer's withdrawal.
"I like to play young guys in the best of five because even at two sets down, I feel I still have my chances," said Djokovic.
"I feel physically fit, I have won most of my five-setters and that experience helps. It's unfortunate for him to have to retire but I could see he was struggling physically."
Rafael Nadal enjoyed a much more serene passage through to the next round when he defeated 19-year-old Jannik Sinner 7-5, 6-3, 6-0.
The 13-time champion reached the quarter-finals for a 15th time and remained on course for a record-setting 21st Grand Slam.
Nadal has now won 104 matches at Roland Garros against just two defeats since his 2005 debut while the Spaniard's latest win extended his run of consecutive sets secured in the French capital to 35.
He will now face Argentina's Diego Schwartzman, who was made to fight for his 7-6, 6-4, 7-5 win over Jan-Lennard Struff of Germany.
The 35-year-old world No 3 is seeded to face old rival Djokovic in the semi-finals.
In the women's draw, Sofia Kenin was added to the list of top names heading for the Roland Garros exit after the fourth seed was thrashed 6-1, 6-3 by Maria Sakkari.
Last year's beaten finalist from the US was the highest seed left in the competition but came up against the in-form Greek who took just 68 minutes to seal victory.
"I'm speechless. I love Paris. I'm having a great time and I don't want to leave anytime soon," said Sakkari, who will take on either reigning champion Iga Swiatek or Ukrainian teenager Marta Kostyuk for a place in the last four.
Meanwhile, Coco Gauff reached her first Grand Slam quarter-final with a superb 6-3, 6-1 battering of Tunisia's Ons Jabeur.
The 17-year-old, who has also yet to drop a set in the tournament, sealed the win in less than an hour and now takes on Barbora Krejcikova. The Czech handed out her own demolition job when she blew away Gauff's countrywoman Sloane Stephens 6-2, 6-0.
"It means a lot to me, especially as I have lost in the fourth round a couple of times so it feels good to get over that hurdle," said 24th seed Gauff.
