Wawrinka's victory sealed second place behind group winner Rafael Nadal and the world number four will play six-time champion Federer in a rematch of last year's stormy semi-final at the prestigious season-ending event at London's O2 Arena.
     
Federer won that meeting in three sets after saving four match points but the game is mostly remembered for reports of a heated post-match row between the players which was allegedly sparked by Federer's wife Mirka heckling Wawrinka and calling him a 'crybaby'.
     
"I'm excited to be back for the semi-finals. It was tough battle," Wawrinka said.
     
"I played a crazy match against Roger in the semi-finals last year. I will try and go and get some rest and be ready," he added.
     
Defending champion Novak Djokovic faces Nadal in the other semi-final earlier today.
     
Nadal leads Djokovic 23-22 in their career head to head while Federer has won 17 of his 20 meetings with Wawrinka.

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