LONDON (AP) -- Roger Federer saved four match points to reach a ninth final at the ATP Finals in a thrilling 4-6, 7-5, 7-6 (6) win over fellow Swiss Stan Wawrinka Saturday.

Having swept his group imperiously, Federer was the favorite, but met strong resistance from the Australian Open champion, who failed to cope with nerves in the end.

Wawrinka had Federer under constant pressure from the baseline, and kept his composure until he served for the match at 5-4 in the deciding set. He dropped his serve following three clumsy approaches to the net on match points.

Federer saved the fourth one with a service winner in the tiebreak then converted his first chance to seal the semifinal.

Federer will face Novak Djokovic in Sunday's final.