London (AFP) - Novak Djokovic on Thursday backed Andy Murray to keep playing despite the insistence of his career-long rival that he is bidding farewell to tennis this year.

Djokovic and Murray have been rivals since they were 12 years old and have clashed 36 times as professionals. That includes seven Grand Slam finals.

“I do wish him all the best in his farewell,” said Djokovic.

“But I wouldn’t be surprised if he decides to come back again. He’s an incredible competitor – resilience that you can definitely study and teach young athletes.”

Murray pulled out of Wimbledon singles after failing to recover from a back operation but is playing men’s doubles with brother Jamie on Thursday and mixed with Emma Raducanu later in the tournament.

The former world number one and three-time major winner said he will retire after the Paris Olympics.

“If this is his last match, obviously it’s sad that he’s not able to finish in his own terms in singles,” said Djokovic.

“Playing alongside his brother is probably even more emotional for everyone – for them, for the family.”

Earlier Thursday, Djokovic was made to fight by British outsider Jacob Fearnley before reaching the Wimbledon third round for the 18th time.

Seven-time champion Djokovic triumphed 6-3, 6-4, 5-7, 7-5 but had to save two break points midway through the fourth set before seeing off the challenge of the world number 277.

“I had never seen him play so there is always the element of surprise,” admitted Djokovic.

“He had nothing to lose and served well. I was a little lucky in the fourth set. I could have won the match in three and it could have gone to a fifth.

“The way he was playing, I’m glad it didn’t.”

- ‘No knee pain’ -

The 37-year-old Djokovic had cruised through the first two sets on Centre Court against a player who was making his Grand Slam debut this week.

He was a break up in the third to lead 3-2 but Fearnley, who was still playing university tennis in the United States until recently, retrieved the break immediately.

He then rode the momentum to claim the third set.

Fearnley forced the 24-time Grand Slam champion to save two break points in the sixth game of the fourth set.

Djokovic made the Briton pay for his failure to convert the advantage and gained a final crucial break in the 11th game before serving out the match.

“I didn’t really feel comfortable in my own skin in the third and fourth sets,” said Djokovic.

“But sometimes you have rough days when you don’t feel your best. It’s a win and I’ll take it.”

Djokovic fired 34 winners past Fearnley, whose 42 winners were cancelled out by an unforced error count of 49.

The Serb said that he was feeling no ill-effects from the knee surgery he underwent after the French Open.

However, he was still wearing a grey knee protector in Thursday’s match.

“I didn’t experience any pain today. The first match I did have one or two situations. Today none, which is great,” said Djokovic who is attempting to equal Roger Federer’s record of eight men’s Wimbledon titles.

World number two Djokovic will take on Australia’s Alexei Popyrin for a place in the last 16.

Fearnley said he would take positives from pushing his illustrious opponent to four sets on his Centre Court debut.

“I’m going to stay down to earth. At the end of the day I lost the match but I’m going to give myself a tap on the back and be, like, ‘Yeah, it was a great summer’,” said the 22-year-old.

“It’s just the start. I’ve been out of college for a month. So, yeah, there’s a lot still in the future. I think myself and everyone on my team is well aware.”