Novak Djokovic had to sweat and dive and bleed, but eventually the world No. 1 found a way.
After dropping the first two sets in tiebreakers to 19-year-old Italian sensation Lorenzo Musetti, Djokovic ultimately prevailed when Musetti retired down 6-7(7), 6-7(2), 6-1, 6-0, 4-0 in the fifth set.
The world No. 1 improved to 31-9 in five-setters and will next face another Italian in No. 9 Matteo Berrettini, who advanced when 20-time Grand Slam champion Roger Federer withdrew from the tournament ahead of their match.
Djokovic has now won 11 straight matches in majors in 2021, including his ninth Australian Open title in February which gave him 18 major titles.
He improved to 15-0 in the fourth round at Roland Garros.
Djokovic remains on track to meet 13-time French Open champion Rafael Nadal in the semifinals Friday. Nadal was set to face another 19-year-old Italian, Jannik Sinner, on Monday.
The big-hitting Musetti played with poise and confidence for two sets, dictating pace with heavy and deep groundstrokes. He improved to 11-0 in tiebreaks as a pro when he won the second set breaker.
But after that Djokovic took over, dropping just four points in a fourth set that lasted just 17 minutes.
In the first game of the fifth set, Djokovic tumbled to his knees while in a baseline exchange but managed to return a forehand from one knee. He then sought treatment for a minor cut on his right hand that drew blood. He still managed to break the Italian for a quick 1-0 lead in the fifth.
At 4-0 down, Musetti retired, sending Djokovic into yet another major quarterfinal.