Justine Henin's 17-match unbeaten run at the Dubai Championships came to an end when she was beaten in the quarter-finals by Italian Francesca Schiavone.
The world number one had won the title on her last four visits to Dubai but put in an erratic display as she lost 7-6 (7-3) 7-6 (7-4).
"She was better, simple as that," said Henin, who had won all seven of her previous matches against Schiavone.
Third seed Ana Ivanovic also went out, beaten 5-7 6-3 6-3 by Elena Dementieva.
Russian Dementieva recorded her third straight win over the Australian Open finalist to book a meeting with Schiavone.
Schiavone looked to have missed her chance when she twice failed to serve out the match in the second set - wasting a match point at 5-4.
But Henin was unable to take advantage, playing a poor tiebreak which Schiavone won 7-4.
"Every point you have to beat her. It's like every point is match point," said Schiavone, whose only previous win over a world number one came against Amelie Mauresmo in the Fed Cup.
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"So at the end when I was in the tiebreak I said you push now or you go home, so it's better that you push now. And I did it.
"To beat Justine you have to play very good, at a high level, and I did today. I think for me it is my best win."
Schiavone will meet Ana Ivanovic or Elena Dementieva in the semi-finals.
In the other half of the draw, second seed Svetlana Kuznetsova booked her place in the last four with a 6-1 7-6 win over Amelie Mauresmo.
The Russian's win means Mauresmo still has not won more than three matches in a row since Wimbledon last year.
"I started to play better in the second set and there were times when I played some good tennis," said the Frenchwoman.
"There were still probably a few things here and there which cost me that second set, and I didn't play the tie-break as I expected, but she came up with some good shots when she needed them."
Jelena Jankovic will play Kuznetsova after opponent Anna Chakvetadze retired from their quarter-final.
Jankovic, celebrating her 23rd birthday, took the first set 6-1 before the Russian pulled out with a left thigh injury.
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