Novak Djokovic's desire has been called into question time and time again during his fall from grace but the defending champion showed there is still fire in the belly at the French Open on Friday.

The Serbian great has suffered an alarming slump since completing a career Grand Slam at Roland Garros last year, struggling to maintain his drive after claiming an elusive title in Paris.

Djokovic lost his status as world number one to Andy Murray late last year and has won just one tournament in 2017.

The 30-year-old said he had been left mentally and physically exhausted after completing a clean sweep of majors in the French capital.

There was a parting of the ways with coach Boris Becker and he recently sacked the remainder of his coaching team in a bid to reinvigorate his career.

He turned to Andre Agassi in a bid to spark a resurgence, the American taking an unpaid role at the French Open - and beyond if Djokovic has his way.

Djokovic has looked disinterested at times, lacking the huge will to win which enabled him to become the dominant force in men's tennis.

Yet there was no shortage of that competitive spirit on Court Philippe Chatrier, where he twice came from a set down to topple Diego Schwartzman in a gripping match which went the distance on day six.

The 12-time grand slam champion demonstrated how much it still matters to him when he had a showdown with the chair umpire, who gave him two time violations and a code violation, and threw his racket down as he was given a stern test by the unseeded Argentinian.

Djokovic regained his composure to pass a stamina test - as he has done so many times over the years - to reach the fourth round and it was notable that he made reference to his mentality several times when speaking to reporters.

He said: "I was mentally still as strong and as calm as I could be, even though I was two sets to one down I kept believing I could break his resistance. It was just too many unforced errors from myself.

"All in all, it was good to be part of five-set match. I didn't play too many of the five-setters the last couple of years. I see a lot of good things in it. I think it will put me in a good place mentally, as well.

"Physically I don't think it's going to affect me at all. You know, I have had many situations like this before where just, you know, having a day to recover is more than enough.

"So, I think mentally it will affect me in a positive way. Hopefully I'll be able to continue, I guess, playing better and better as the tournament progresses."

Albert Ramos-Vinolas will aim to put that mental strength to the test again in the last 16.