Del Potro upsets Federer to progress

Paes-Stepanek work their way past Bryan twins

Juan Martin del Potro beat Roger Federer 7-6, 4-6, 6-3 to reach the semifinals of the ATP World Tour Finals on Saturday.

The Argentine guaranteed himself one of the top two places in Group B with a 2-1 record, the same as defending champion Federer who had already sealed a semifinal spot after winning his opening two round-robin matches at the season-ending tournament.

The final day of action in Group B began with seven scenarios, but a three-set win for world number seven Del Potro muddied the waters as the line-up for the semifinals will now not be known until after the match between David Ferrer and Janko Tipsarevic.

Victory for Tipsarevic would see Del Potro top the group while a win for Ferrer would mean three players are tied on two wins and in that case Federer would top the group because of his superior sets percentage and Del Potro would be runner-up. Ferrer had been relying on a Federer victory to keep his hopes of a semifinal place alive.

The winner of the group will face Britain's Andy Murray while the runner-up will play world number Novak Djokovic. On Friday, Djokovic beat Czech Tomas Berdych 6-2, 7-6 and Murray later overcame Frenchman Jo-Wilfried Tsonga by the same score to ensure that no calculators would be required to decide the semifinalists.

Djokovic finished the group stage with an unblemished record to top the standings and it meant Murray only had to win a set against Tsonga in the evening to progress — a feat he accomplished in 33 minutes.

Murray had to save a set point in the second set of his match against Tsonga, although by that stage the US Open champion's place in the semifinals was assured. Tsonga, despite losing his opening two round-robin matches, could have reached the semis at Murray's expense with a straight sets knockout but a loose start scuppered any hopes he had.

Murray meets Muamba

After the match, Murray met former Bolton Wanderers soccer player Fabrice Muamba, who had suffered a cardiac arrest playing against Tottenham Hotspur in an FA Cup tie in March and needed life-saving treatment after his heart stopped beating for 78 minutes.

"I remember exactly where I was when it happened," Murray said. "I was watching the match on the TV in the States. Yeah, I sat in front of the TV. There was nothing on the TV. I just couldn't believe it happened.”

Paes-Stepanek dazzle

Leander Paes and Radek Stepanek will go into the semifinals of the ATP World Tour Finals in confident manner as they pipped the top seeds Bob Bryan and Mike Bryan in their last Group A match on Saturday for an unbeaten record.

Third seeds Paes and Stepanek held their nerves to beat three-time champions 6-4 6-7(6) 10-7 in one hour and 45 minutes.

Now Bryans would be praying that seventh seeds Aisam-Ul-Haq Qureshi and Jean-Julien Rojer beat fifth seeds Marcel Granollers and Marc Lopez, so that they move to the next stage.

Paes and Stepanek broke both Mike and Bob in the third and fifth games respectively to take a 4-1 lead. Stepanek committed a double fault to lose his service game but closed out the set with a wonderful backhand volley that angled away from Bob.

There were no service breaks in the second set, and the American twins won it on a tie-break. In the 16-minute Match tie-break, Paes and Stepanek took a 6-4 lead and maintained the two-point cushion. At 9-7, Mike Bryan returned into the net.