Another fine display from the veteran carried him to the win as he set up a clash with Novak Djokovic in a repeat of the round-robin meeting he won earlier in the week.
It looked set to be a difficult evening for Federer when Wawrinka secured the first break in the fifth game, but errors from the back of the court opened the door to the third seed, who fought back to 4-4.
Wawrinka was unable to hold his nerve while serving to stay in the opener, with a double fault and two miscues gifting Federer the first set.
The French Open champion found it difficult to shift the momentum, and another service game filled with errors allowed Federer to break again early in the second set.
A comeback soon looked unlikely as Federer found his rhythm on serve to hold off his opponent, and the victory was clinched with another break as the 34-year-old kept his bid for a seventh Tour Finals win alive. body check tags ::