FILDERSTADT, Germany -- Martina Hingis was upset Thursday by Elena Dementieva 6-3, 6-1 in the second round of the Porsche Grand Prix.

In two other upsets, Russia's Tatiana Panova beat third-seeded Jelena Dokic 1-6, 6-4, 6-1 and Myriam Casanova upset fourth-seeded Justine Henin 7-5, 4-6, 6-4.

"Physically I'm feeling better but there are still ups and downs," Hingis said. "I feel quite a bit better than last week and for six games I was able to keep it up, and after that I was a little flat, a little tired. But there was no reason for that. A match lasts two sets, not just six games."

Meanwhile, Kim Clijsters breezed into the quarterfinals with a 6-1, 6-2 win over Iva Majoli and fifth-seeded Amelie Mauresmo beat Anne Kremer 6-1, 6-2.

The seventh-seeded Hingis didn't look sharp enough in her fifth tournament since ankle surgery in May.

"After a long layoff like that, I'm just missing the stamina,'' Hingis said. "But I'm healthy, everything is OK. You just have to grit your teeth to get back to the top.''

Dementieva took advantage with her baseline play.

"I know Martina was injured and had it hard, but I also played well,'' Dementieva said.

Clijsters turned in her second impressive performance at the event. In her first-round match, Clijsters easily overpowered Anastasia Myskina 6-4, 6-2.

"I knew I had to apply pressure right from the start against Majoli, because if she can play her own game, she's tough,'' Clijsters said.

Information from Reuters was used in this report.