The pair have won nine Wimbledon titles between them, contesting three finals against each other at the All England Club, and it is no surprise to Djokovic that they continue to challenge for major honours.

“I think they are two different players, two different characters,” Djokovic said.

“Both are extremely successful, really impressive as champions on and off the court in their own way.

“Roger has always taken care of his body and the scheduling.

“Obviously technically, he’s probably the best player in the world.

“When he plays, it looks so easy, it looks so flawless.

“I think the kind of game that he has, the proper care that he had about his body and professionalism has kept him so durable, kept him at the top of the men’s game for so many years. He’s still up there.

“And Rafa on the other side, he’s somebody that spends a lot of hours on the court.

“He really loves to practise for two, three hours in a row. He is just somebody that has a hard working ethic. It really pays off.”

Djokovic again found himself dismissing allegations of cheating after the world number one beat Philipp Kohlschreiber in straights sets on Monday.

The Serbian, who now faces Finland’s Jarkko Nieminen in the second round, came under fire after his coach Boris Becker suggested they had secret signals to communicate with each other during matches.

ATP rules state players are not allowed to receive “communications of any kind, audible or visible” during a tournament match and Djokovic was visibly annoyed when the issue was raised again in his post-match press conference.

“I don’t understand what you really want,” said Djokovic, who won 6-4 6-4 6-4 on Centre Court. “Do you want to say I’m cheating, my team? I’m really trying to figure out what’s behind this.

“I mean, are you asking only me or are you asking other players, as well?

“I’m going to say that there are certain ways of communication which is encouragement, which is support, which is understanding the moment when to clap or say something that can lift my energy up, that can kind of motivate me to play a certain point. But it’s all within the rules.”

Djokovic added: “Of course, I accept the fact if my coach, Boris or Marian, do something that is against the rules, I have no complaint about the code violation that I get for coaching.”

In the women’s draw, Petra Kvitova launches the defence of her Wimbledon crown against Holland’s Kiki Bertens, while last year’s semi-finalist Simona Halep plays Slovakian Jana Cepelova.

Both players are hoping to stop Serena Williams from taking another step closer to a calendar Grand Slam, after the American triumphed in both Australia and France earlier this year.

Williams beat Russian qualifier Margarita Gasparyan in straight sets on Monday and the 33-year-old acknowledges how far she has come since losing in the third round at Wimbledon a year ago.

“I’ve had such an amazing year, I ended up winning the (US) Open, the (WTA) Championships, the Australian and France,” Williams said.

“I couldn’t have dreamt of a better 12 months. So it’s been really great. I’m just excited about that and really focusing on that.”