Novak Djokovic relishing Alexander Zverev test after firing warning at ATP Finals rivals with dominant win

If Novak Djokovic’s tennis wasn’t warning enough to Alexander Zverev ahead of their meeting on Wednesday then the world No1’s assessment of his form and fitness showed the young pretender just what he is up against.

Djokovic, the overwhelming favourite to take the ATP Finals crown on Sunday, began his bid to end a remarkable six months on one last high in style on Monday night, swiftly dismantling John Isner in a 6-4, 6-3 victory without breaking much of a sweat.

Up next for the 31-year-old is young pretender Zverev, who was given a more comprehensive workout in victory over Marin Cilic, and it is a contest Djokovic is relishing.

“I'm not too exhausted. I'm feeling fit physically and mentally,” he said. “I'm looking forward to that match. The good thing about this tournament is that you have days in between matches, and you're guaranteed to play three matches in the group.

“I obviously put myself in a very good position with the group with a straight-sets win.

“Playing Zverev, who also had a straight-sets win [on Monday], I look forward to that. It should be a great match. I think we played against each other only twice. We split wins.

“I played him recently in Shanghai, but wasn't at his best. I expect him to play better than he did then.”

The state of the O2 court has provoked much debate through the first two days of the tournament, with Roger Federer branding them “definitely slower” before Zverev countered that they were “very fast”.

You sense for a player hitting the ball as smoothly as Djokovic it doesn’t particularly matter how fast the ball is moving off the deck.

“My results here have been pretty good in the last 10 years. So can't complain too much. Although it takes a little bit of time really to get yourself adjusted to the surface because the surface is a good surface.

“But, you know, it takes a lot of rotation, takes a lot of spin. When you serve well, also it accelerates through the court.

“You kind of always have to be on alert, be very solid in your core, I would say, to be able to execute your shots well and constantly adjust with your feet to the ball. The surface kind of makes you work more. That's why probably players feel like it's a bit tricky, demanding.”

Djokovic found the court to be nothing of the sort, hitting 21 winners to six unforced errors and serving six aces to a single double fault.

More impressive was how the Serb neutered Isner’s greatest weapon, his powerful serve, keeping the American to a relatively meagre 66 per cent of first serves won.

Isner did not mince his words in assessing how the preceding hour and 13 minutes had panned out.

“I got my ass kicked.

“That was pretty comprehensive out there. Certainly there are some things I have to try and keep improving and the beauty of this format is I'm definitely still alive. I was the underdog and got beat down pretty good.

“[As a returner] he is No.1 and No.2 and No.3. He's the best returner I've ever faced for sure.”