Roger Federer bounced back from his opening-day shocker against Kei Nishikori by sweeping aside Dominic Thiem at the ATP Finals.

The 37-year-old six-time winner knew anything other than victory would see him fail to qualify for the last four for only the second time in 16 appearances at the O2.

But it was a vastly more upbeat Federer who pulverised Thiem 6-2 6-3 than the grouchy character who had trudged off court after an error-strewn defeat by Nishikori 48 hours earlier.

Roger Federer in action against Dominic Thiem
Roger Federer in action against Dominic Thiem (Adam Davy/PA)

Afterwards Federer put his upturn in fortunes, and mood, down to cancelling a scheduled practice session on Monday – and he will repeat the trick on Wednesday.

“I will do the same again because it worked,” he said. “It was not about my forehand, or my backhand, or my serve or anything. I guess it was my head. For that sometimes you need a break.”

The 20-time grand slam champion still needs to beat the in-form Kevin Anderson, who knocked him out at Wimbledon and who dropped just one game against Nishikori in Tuesday afternoon’s match, if he is to clamber out of the group.

Federer grabbed a break in the third game against a nervous-looking Thiem and a second for 5-2 on his way to taking the first set.

Thiem, who also lost his first match to Anderson, dropped serve at the start of the second set and again at the end as Federer wrapped up victory in an hour and six minutes.

Federer also broached the subject of a mild stir caused by French doubles player Julien Benneteau, who this week claimed he sometimes recieves preferential treatment and favourable scheduling, in particular when he won this year’s Australian Open.

“I get asked would you like to play Monday or Tuesday sometimes,” said Federer. “Sometimes I get asked, do you want to play day or night?

“Sometimes we have our say. But I asked to play Monday at the US Open. I played Tuesday night. It’s all good.”

Anderson had previously underlined his credentials as a major contender in London with a brutal destruction of Nishikori.

Japanese world number nine Nishikori was on cloud nine after stunning Federer, but he was brought crashing back down to earth by the O2 debutant.

Nishikori was staring down the barrel of the ultimate humiliation, and only the second 6-0 6-0 defeat in the history of the Finals, following a ruthless display by the South African.

Yet at 6-0 5-0, and with less than an hour on the clock, the 28-year-old finally managed to string four serves together to get on the scoreboard and avoid the dreaded ‘double bagel’.

It only delayed the inevitable, though, as Anderson duly served out for a 6-0 6-1 victory in 63 hopelessly one-sided minutes.

“That’s amongst the best matches I’ve played,” said Anderson, who is in pole position in the group although qualification for the semi-finals is still possible for all four players.

Meanwhile, Britain’s Jamie Murray and Brazilian partner Bruno Soares clinched their place in the semi-finals of the doubles for the third straight year.

Murray and Soares ran out 6-4 6-3 winners against Colombian duo Juan Sebastian Cabal and Robert Farah to ensure their progress with a match to spare.