Roger Federer has admitted that he is now fully fit and ready to go all out to win the ATP World Tour Finals in London. The Swiss ace was speaking after his straight-set win over Jack Sock in the first group stage match at the O2 Arena.

The 36-year-old admitted that he was unsure of his fitness levels coming into the tournament as he took a long time to recover from his exertions at Swiss Indoors, which he won after beating Juan Martin del Potro in the final.

Federer pulled out of the Paris Masters, which was a week prior to the tournament in London, and revealed that he did not practice too much during the week in order to rest and recover for the ATP Finals. He played an exhibition match with Andy Murray on 7 November and admitted that it served as a minor part of his preparations for the ongoing event.

The 19-time men's singles Grand Slam champion came through his first match with relative ease, winning 6-4, 7-6 in one hour and 31 minutes. Federer believes the first game has put him in good shape for the rest of the tournament – one that he is keen to win to end the season on a high. He faces Alexander Zverev on Tuesday, 14 November, and then will take on Marin Cilic in his final group stage game.

"It took me long time to recover really, to be honest," Federer said, following his victory over Sock, as quoted by the Express.

"I had a very slow week, the Paris week. But also, other than the charity match, the Andy Murray Live match in Scotland, I also didn't do that much. The last sort of Thursday, Friday, especially Saturday, were my more intense days. Other than that, I didn't do much," the Swiss tennis legend revealed.

"I'm happy that I was able to come out today and had actually good energy. This is the best I've felt since the Del Potro final. I'm very happy to see that I didn't have to pay the price for taking it easy, you know, resting, recovering. But then turning it up the last few days got me in shape for today.

"Now I think I'm in the tournament. Now there's no more turning back. Just full steam ahead every match that comes," he added.

Roger Federer
Roger Federer beat Jack Sock in his first group stage match at the ATP World Tour Finals in London on Sunday, 12 November Getty