Roger Federer admitted it was a new sensation having to respond so quickly to defeat after he swept aside Dominic Thiem 6-2 6-3 at the ATP Finals in London.

The Swiss – a six-time winner of the event – 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.

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

It was a similar tale in the second set, with the 37-year-old in attacking mode as he wrapped up victory in a little over an hour. Federer must now defeat in-form Kevin Anderson to make the semi-finals.

The South African thrashed Kei Nishikori 6-0 6-1 – with the Japanese narrowly avoiding the dreaded ‘double bagel’ – to add to his win over Thiem.

For Federer, it was a big positive to turn things around quickly after losing his opener to Nishikori in uncharacteristic style.

“It feels good, I’m very happy I showed a reaction after the last match against Kei,” he said.

“No match is easy here and it’s not something I’m used to, losing and then coming back and playing again, but it’s a great challenge and I’m happy with my attitude and how I played.

“I was more positive, more happy on the court and I reminded myself what a privilege it is to play here at the O2.”

Federer is now 6.00 to win the ATP Tour Finals, with world number one Novak Djokovic favourite at 1.36.