Perhaps wary of the gruelling quarterfinal clash between the pair at Wimbledon, which he lost after winning the first two sets, Federer swatted away South Africa's Kevin Anderson 6-4, 6-3 with minimal fuss on Thursday.

The six-time ATP Finals champion started this year's event slowly, with a loss to Kei Nishikori, but knew that taking a single set would be enough for him at the 02 Arena, after Dominic Thiem - who Federer beat on Tuesday - had beaten Nishikori earlier in the day (see below).

I'm very happy," said Federer, 37, after the victory. "The first match was tough against Kei, I never got going. With my back against the wall maybe it is easier for me to play.

"I tried to come up with a good game plan against Dominic and also Kevin today. I'm happy it all worked out. I'm thrilled to be in the semis."

Both players broke serve early in the opening set before Federer's class began to shine through, much to the delight of a partisan London crowd. 

With a semifinal in the bag, the 20-time Grand Slam champion opened up a bit and Anderson had no answer. But after wins in his opening two matches, the big South African will join Federer and Novak Djokovic in the semifinals. The last spot will be taken by Alexander Zverev, Marin Cilic or John Isner.

Thiem opens account but goes home

Dominic Thiem's 6-1, 6-4 win over Kei Nishikori may ultimately have meant nothing but, for a few hours, it gave the Austrian a chance to stay alive and escape the group stage for the first time in his career.

Thiem broke Nishikori for a 2-0 lead early on but was forced to save four break points before cementing a 4-1 advantage and going on to seal the first set.  Nishikori improved slightly in the second set but still couldn't stop the sixth seed claiming the straight sets win he required to put some pressure on Federer.

"I didn't come into the match with too much pressure," said Thiem after the win. "I just wanted to show to myself and all the spectators the real Dominic Thiem."

Thiem's positive finish to the event was in stark contrast to Nishikori, who was brilliant in beating Federer in straight sets in his opener before losing four sets in a row against Anderson and Thiem, winning just six games in the process.