Defending champion Lindsay Davenport was beaten in the quarter-finals of the Porsche Tennis Grand Prix on Friday, losing 4-6 6-3 6-4 to sixth-seeded Kim Clijsters.

But fifth seed Amelie Mauresmo of France reached her third successive semi-final when she overcame the tenacious Tatiana Panova of Russia 6-3 6-4.

Second seed Davenport seemed to be in control against Clijsters, making few unforced errors and pressuring the Belgian with her intimidating serve.

But a few mistakes crept into Davenport's game midway through the second set, and she was broken with a lob to go down 4-2.

At the end of the second set Davenport left the court to have her left thigh strapped and she was clearly hindered in her movement in the third.

Casanova crashes

Barely going for the ball when pulled to either side Davenport dropped her serve for 1-0, and although she managed to continue playing she was unable to make any impression.

Earlier, Daniela Hantuchova ended the run of American qualifier Alexandra Stevenson with a crushing 6-1 6-2 victory.

Swiss qualifier Myriam Casanova was also unable to follow up her second round upset of fourth seed Justine Henin when she was beaten 6-2 6-3 by Elena Dementieva.

Although Stevenson took advantage of a weak service game from Hantuchova to lead 2-0 in the second set, the eighth-seeded Slovak swept the final six games.

Dementieva sped to a 4-0 lead against Casanova in the first set as she opened up some winning angles in the hard-hitting baseline rallies.

Although Casanova settled and offered stronger resistance during the remainder of the match, it was Dementieva who held on for victory in a match littered with errors.

Quarter-final results (numbers represent seedings):

K Clijsters (6-Bel) bt L Davenport (2-USA) 4-6 6-3 6-4
A Mauresmo (5-Fra) bt T Panova (Rus) 6-3 6-4
D Hantuchova (8-Svk) bt A Stevenson (USA) 6-1 6-2
E Dementieva (Rus) bt M Casanova (Swi) 6-2 6-3