Berlin: Dinara Safina ended Serena Willaims' 17-match winning streak with a 2-6, 6-1, 7-6 (5) victory on Friday to reach the German Open semi-finals.
The 17th-ranked Russian kept pressuring Serena's backhand, the same tactic that worked a day earlier in an upset of top-ranked Justine Henin.
Both players held serve throughout the final set, before Serena let a 4-3 lead in the tiebreaker slip away and sent a forehand long and wide to end the two-hour match.
"It's not like I played my best and lost, it could be worse," Serena said. "I can sit here and name 50 things I could do better."
Serena, chasing a fourth straight title, appeared poised to improve on a 21-1 record this year without trouble until Safina's hard shots began to land in the second set.
"I couldn't concentrate, I started the match like, 'I won yesterday,' so that was good," Safina said. "Then I started believing I could win. I just had to be more aggressive."
Serena was the 10th top-10 victim for the 22-year-old Safina, the sister of two-time grand slam champion Marat Safin.
"I think she's playing far better than in the past," Serena said.
With the many upsets at the German Open, where 17 of the world's top 20 players started, Serena said it will be hard to name a favourite for June's French Open.
"I'm excited I lost here and not in Roland Garros," Serena said. "The pressure is off me."
After a slump in 2007, Safina said last month's win against Lindsay Davenport at the Sony Ericsson Open restored her belief in her ability to beat the top players.
Safina said her brother sent a "Roll on, sister" SMS after the win against Henin, a four-time French Open champion.
Safina now has beaten most of the best players, a list that includes Maria Sharapova and Lindsay Davenport. But the Russian said she didn't see herself among their ranks soon.
"I'm No. 17. It's such a long way," Safina said. "How far I can go? Only God knows."
When Safina raised her game in the second set, she broke serve twice, whipping a shot past Serena at the net to take a 4-0 lead.
She will face Victoria Azarenka in Saturday's semi-final, after the 18-year-old Belarusian ousted 15th-seeded Alona Bondarenko 7-6 (2), 6-2.
World No. 2 Ana Ivanovic of Serbia entered the semi-finals on Saturday with a 3-6, 6-4, 6-3 win over 10th seeded Hungarian Agnes Szavay.
She will will play Elena Dementieva, seventh seed, in the semi-final on Saturday.