Vlxi Tech

Roger Federer fought back Saturday to reach the semifinals in the ATP World Tour Finals.

On the back of a poor season, the 17-time Grand Slam winner overcame a 3-0 deficit in the third set to beat Juan Martin del Potro 4-6, 7-6 (2), 7-5 to reach the semifinals for the 11th time.

The Swiss earned a chance to prove that — despite his aging legs, aching back and recent lack of consistency — he can still beat rival Rafael Nadal, his semifinal opponent.