Injury-hit Novak Djokovic digs deep to make French Open last eight

Novak Djokovic limped into the quarter-finals of the French Open after defying a knee injury to come through the longest Roland Garros match of his career.

The defending champion defeated Francisco Cerundolo - in another five-setter - 6-1 5-7 3-6 7-5 6-3 in four hours and 39 minutes.

World number one Djokovic blamed the slippery court for the injury he appeared to sustain at the start of the second set.

He began grimacing and rubbing his right knee shortly after taking the first set and required a medical time-out at 2-1 down in the second.

Djokovic was heard telling the physio: "I screwed up my knee. I'm slipping and sliding all the time."

Four games later he complained to a tournament supervisor about the state of the court, saying: "I'm telling you as a player, it's not OK."

When the official told Djokovic the grounds people felt the surface was fine, the Serbian snapped: "They know better than me the court is good or not?"

The 37-year-old took medication again after Argentinian 23rd seed Cerundolo (above) levelled the match, finally converting a break point at the 13th attempt.

Cerundolo also took his 14th at the start of the third set as Djokovic continued to hobble between points.

The 24-time grand slam champion, whose five-set match against Lorenzo Musetti finished after 3am on Sunday morning, appeared to be running on empty and chuntered with his team in the players' box, occasionally appearing to suggest he was ready to give up.

Yet he retrieved a break in the fourth set and then took the match to a decider, letting out a huge roar as Cerundolo dunked a forehand into the net.

Suddenly Djokovic was moving freely again and broke at the start of the fifth, only to be immediately pegged back.

His mood darkened yet further when