Third seed Ana Ivanovic was pushed all the way by Venus Williams before edging to a 7-6 (7-3) 6-4 victory in a tense Australian Open quarter-final.
Neither player could hold their serve in a pulsating first set, which Ivanovic eventually won in a tie-break.
Williams came out fighting in the second, but was reeled in by Ivanovic's punishing forehand, and the Serb held her nerve to close out the match.
Ivanovic will play Slovakia's Daniela Hantuchova in the last-four.
Hantuchova, 24, marched into her first Grand Slam semi-final by thumping Polish teenager Agnieszka Radwanska.
Radwanska, 18, looked nervous early on and Hantuchova took full advantage, dictating play from the baseline, and running away with the first set.
"I'm just so happy I pulled through the whole two sets - it was an amazing match"
The Slovakian kept up the tempo in the second, destroying Radwanska's serve, and quickly closed out a 6-2 6-2 victory.
That match was completely one-sided but Ivanovic had to work much harder to end the challenge of Williams, the eighth seed, in one hour and 46 minutes.
Both players were returning serve ferociously and it was not a great surprise that there were six breaks in the first set.
But it was Williams who was making more unforced errors, with her backhand volley particularly unreliable, and two of them ended up in the net in quick succession as Ivanovic took the tie-break.
The former world number one was stung into action and, briefly, her serve regained its reliability to help her move 3-0 up in the second set.
Ivanovic kept her cool, however, and some stinging cross-court forehands helped her break back and move level again.
The accuracy of the Serbian's groundstrokes was the difference between the two players and two more mistakes from Williams gave Ivanovic another break at 5-4.
Williams raised her game again but Ivanovic served her way back to deuce before closing out a famous victory, her first over the American in five attempts.
"I'm just so happy I pulled through the whole two sets," Ivanovic said. "It was an amazing match, we had lots of long rallies, she's an amazing competitor and she was also playing very well today."
Ivanovic, who has family living in Melbourne, was roared on by a vocal crowd at the Rod Laver Arena and was quick to pay tribute to her fans.
"It's amazing, thank you guys so much, you helped me get through that second set," the 20-year-old said. "Most of all I'm thrilled that it happened here because I just love playing here and I'm so comfortable here on court."
Williams, meanwhile, refuted claims that her defeat was further indication that she is a waning force in women's tennis.
"I've got nothing to lose. I'm in a great position. I'm feeling like I'm playing well"
"There has been a lot of talk every single year," she said. "I think what's important to me is what goes on in my head. I've been a champion.
"I have full expectations and aspirations to continue to play high-quality tennis and to continue to be a champion."
Hantuchova is looking forward to meeting Ivanovic, saying: "I've got nothing to lose. I'm in a great position. I'm feeling like I'm playing well.
"I'm just really looking forward to be out on the court again, giving my best and seeing what happens."
Maria Sharapova takes on Jelena Jankovic in the other women's semi-final.
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