Novak Djokovic's epic fourth-round victory at the French Open ...

Novak Djokovic said that he had doubts about whether he would finish his marathon fourth-round contest against Francisco Cerúndolo at the French Open, such was the extent of the knee pain he was managing throughout the match.

Djokovic prevailed 6-1 5-7 3-6 7-5 6-3 in a pulsating encounter against the Argentinian world No. 27 on Monday, his second consecutive five-set match after a brutal 3 a.m. finish against Italy’s Lorenzo Musetti in the third round.

The defending champion’s victory against Cerúndolo ended much earlier, but it did take longer to complete, wrapping up in four hours and 39 minutes. This was also his 370th victory at a grand slam, breaking Roger Federer’s record for the most wins at major tournaments.

And while Djokovic showed phenomenal resolve and perseverance to come back and win when he trailed by a set and a break, he admitted to having concerns about pain in his right knee, which he said only subsided once his medication had kicked in.

“At one point, I didn’t know, to be honest, whether I should continue or not with what’s happening,” the Serbian world No. 1 told reporters.

“I got the medications, and then after the third set was done, I asked for more medications and I got them … I’m glad that I was able to play the fifth set and the last three or four games of the fourth without feeling that pain that I felt for two and a half sets, but you never know what will happen tomorrow.”

Djokovic receives treatment to his knee during the victory against Cerúndolo. - Antonio Borga/Eurasia Sport Images/Getty Images

Djokovic dominated the first set and looked on course for a comfortable victory until he tweaked his knee at the start of the second set.

He continued playing after a medical timeout but later acknowledged that his movement was hampered, particularly when he was forced to make a sudden change of direction or race to the net to retrieve a drop shot.

It was only near the end of the fourth set when Djokovic, aiming to win an outright record 25th grand slam singles title at the French Open, was able to move without pain and raise his game.

A crucial break of Cerúndolo’s serve at 4-3 in the fourth helped to swing the momentum in his favor, before a further break at 6-5 concluded an absorbing set in just over an hour to level the match.

The pair traded breaks at the start of the deciding set but Djokovic struck the decisive blow soon after, breaking Cerúndolo at 4-3 and seeing out the match the following game.

The 37-year-old later said that persistent rain in Paris had made the courts more slippery than usual. He had asked for the clay to be swept more regularly during the fourth-round match, though his request was rejected.

“I slipped way too many times,” Djokovic told reporters. “That is quite unusual … I’ve slipped and fallen on the clay many times in my life, and on grass as well, but this was just too many times today.

“I’ve had a conversation with the chair umpire where I just asked would it be possible to sweep the court – I understand not every changeover – but every second, every third changeover? Not to wait for a set to finish but to have slightly more frequent care of the court … The answer was no.

“Could this injury have been prevented?” he added. “Possibly, if there was just a little bit more frequent care of the court during the set. That’s basically all I asked for.”

CNN has contacted French Open organizers for further comment.

After coming through two grueling matches – his first back-to-back five-set matches at Roland Garros since 2012 – Djokovic will face Norwegian seventh seed Casper Ruud in the quarterfinals on Wednesday.

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