World number one Novak Djokovic stayed on course to become the first man in over 50 years to win all four Slams twice but only after fighting back from two sets down to see off 19-year-old Lorenzo Musetti.
Musetti, ranked 76 and making his Grand Slam debut, was poised to condemn Djokovic to his earliest exit in Paris since 2009 when he captured the first two sets, 7-6 (9/7), 7-6 (7/2).
But Djokovic levelled by taking the next two, 6-1, 6-0 before Musetti, who had needed a medical time-out, retired at 4-0 down in the decider suffering from cramps and a back injury.
“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 18-time major winner Djokovic.
“I feel physically fit, I have won most of my five-setters and that experience helps.”
It was the fifth time in his Grand Slam career that 34-year-old Djokovic has come back from to sets down.
Djokovic, the 2016 champion and chasing a 19th major, reeled off 53 of the last 61 points as he made a quarter-final at the majors for the 49th time.