London, Nov 27 (DPA) Roger Federer and Juan Del Potro qualified in nail-biting style for semi-final places in the ATP World Tour Finals, with Scot Andy Murray kept from a spot by the tyranny of mathematics.
Federer won Group A despite taking a loss in his Thursday match to Del Potro 6-2, 6-7 (5-7), 6-3, a result which eliminated Murray on winning game percentage despite his earlier defeat of Spain’s Fernando Verdasco 6-4, 6-7 (4-7), 7-6 (7-3).

The maths could not have been more complex for places at the weekend at the eight-man season wrapup.

Murray needed a three-hour struggle to tighten the race in the afternoon, but had to wait to learn his fate until Federer’s night-time clash, which ultimately sealed the group fate.

Federer has now taken a second straight loss to the Argentine, who stole his US Open title two months ago.

The results mean that only one place in the semis remains to be decided.

Besides Federer and Del Potro, Swede Robin Soderling took a spot on Wednesday as he defeated Novak Djokovic to post a perfect group record of two wins and four sets.

Rafael Nadal crashed out with his loss to Nikolay Davydenko, with play in the group to conclude Friday.

“It was tough, but I needed to win the match,” said Murray. “I had to focus on that.”

Group play wraps up Friday as number two Nadal plays Soderling’s most recent victim, Novak Djokovic, and Davydenko plays Soderling.

Murray had to scramble until the end to subdue Verdasco, a victory which produced 18 aces for the Scot.

Murray’s conversion percentage on the day was poor, with the home hero managing on just one of 13 break point chances.

“I was just trying to win the points, trying to play good,” said the Spaniard.

“Some days you don’t win the break points, some days you win the break points. Every match is different. There are some matches that first point you have against you lose, and in another match you have 10 or 12 and you win all 12. Tennis is like that.”

Murray struck 39 winners and 28 unforced errors, finally getting a grip on the high-voltage marathon as a Verdasco double-fault sent the Spaniard to a 2-4 tiebreak deficit in the final set tiebreaker.

Murray soon managed three match points, converting on the first as a Verdasco volley at the net touched just wide.

“He played ridiculous on the big points in the second set, and to a certain extent in the third set, as well,” said Murray.

“He served huge. When someone hits close to the line on these courts it’s tough because the ball stays very low, and you have to hit up. He was able to dictate the points, staying strong.”