Federer gains semi date with Nadal

Six-time champion Roger Federer rallied past Juan Martin del Potro 4-6, 7-6 (2), 7-5 on Saturday to reach the semifinals of the ATP World Tour Finals for an 11th time and set up a clash against top-ranked Rafael Nadal.

Novak Djokovic, who defeated Richard Gasquet in three sets, will take on debutant Stanislas Wawrinka in the other semifinal at the year-end tournament.

Both Federer and del Potro needed a win in their final round-robin match to progress from Group B and treated the crowd to a tense and entertaining back-and-forth match. Federer trailed in all three sets before coming out on top.

"I don’t get a day off, I’ve got to back it up and be ready to go again tomorrow," Federer said. "I’ll try to make his (Nadal’s) life a bit difficult."

Only once in 12 appearances has Federer failed to advance to the last four at the season-ending tournament for the top eight players. The 17-time Grand Slam winner has endured a disappointing season and the elite event is his last chance to win a big title in 2013.

Federer had a slow start, struggling to return del Potro’s big serve in the first set and committing seven forehand mistakes as his rival opened up a 5-1 lead.

Federer came back and broke del Potro at love as he served for the set but the Argentine former finalist saved two break points in his next service game before closing it out.

Capitalizing on his opponent’s errors, del Potro broke again in the third game of the second set when Federer’s backhand hit the net.

The Argentine looked set for an easy win but failed to build on the momentum, double-faulting as Federer leveled at 3-3.

Federer then gradually took the upper hand with a brilliant display at the net and played a nearly prefect tiebreaker as del Potro crumbled, clinching the set with an ace.

But Federer again started sluggishly in the decider, allowing del Potro to break as he hit two consecutive weak forehands.

But the blip was temporary and, once again, his rival could not take advantage of his inconsistency. At 3-1, del Potro saved a break point but fluffed a forehand on the second one, bringing Federer back into the match.

Hitting more confidently towards the end, Federer broke to go up 6-5 and saved a break point in the next game before closing out the match with his 10th ace.