Basel - Juan Martin del Potro struggled into the Swiss Indoors semi-finals on Friday by beating South African Kevin Anderson 3-6, 7-6 (7/3), 6-2, a day after qualifying for the year-ending World Tour Finals.
The second seed was pushed all the way by his opponent, who used his big serve to good advantage during a match which stretched over two hours.
Del Potro, playing only his second event since coming back from a month off to heal a left wrist problem, seemed to be feeling his back on occasion, a legacy from when he won the Vienna title last weekend.
"It was tough to find my way into the match, he played well at the start," said Del Potro, who added that his back was not a real problem.
"I was lucky to stay in the match in the tiebreaker. But the third set was a lot easier than the first two. I played really well then, broke him twice and got some confidence.
"I stayed calm in the third set, that was the key to this match, trying to remain calm all the time on court."
The Argentine will take a 4-1 record into his Saturday semi-final against French third seed Richard Gasquet, who kept alive his bid to secure one of the two remaining places in the World Tour Finals with his 6-2, 7-6 (7/5) defeat of sixth seed Mikhail Youzhny.
Del Potro has beaten the French player twice in 2012, including the Estoril final on clay last May and indoors in Marseille in February.
"I'm not thinking about London yet, only about trying to play a couple of more matches here," said the South American.
"I'd love to be in the finals here. But I need to play better tomorrow if I want to win."
Gasquet trails three rivals in the points chase to the season wrap-up in London from November 5, standing adrift of conpatriot Jo-Wilfried Tsonga, Serb Janko Tipsarevic and Spain's Nicolas Almagro.
Of the three, Tsonga and Tipsarevic quit first-round matches due to injuries in Valencia while Almagro reached the quarter-finals but lost to David Ferrer on Friday.
Gasquet broke three times in his straightforward win over Youzhny, a fellow former top 10 player. The loss in one and three-quarter hours denied the Russian his 400th career match win.
Gasquet pronounced himself confident after a solid victory, his third in seven meetings with Youzhny.
"I fought a lot and played a good match," said the winner. "I'm excited to try for a place in London. It's been five years since I played the year-end finals (in Shanghai).
"It would be really nice to be a part of it again, but I need to win some more matches this week and next in Paris."
Later Friday, top seed and home hero Roger Federer, who is looking for his sixth title at the event from the last seven editions, was taking on another Frenchman in Benoit Paire.
Paul-Henri Mathieu of France was playing Bulgarian Grigor Dimitrov for a semi-final place.
The Frenchman was hoping to reach his second semi-final since returning in late January after missing all of 2011 with a right knee injury.