Italy's Flavia Pennetta stunned Wimbledon champion Venus Williams with an impressive 6-4, 7-6 win to reach the Bangkok Open final on Saturday.
Pennetta held her nerve as the second-seeded American launched a determined fightback, the Italian emerging victorious in a marathon second set tiebreak to end her opponent's hopes of reaching a third straight WTA final.
"That was one of the most beautiful wins of my career," Pennetta told reporters.
"When she came back, I started to think I'd lost my chance to win. I knew it would be a tough match. I was a little nervous but I played good tennis."
Pennetta, ranked 49th in the world and winner of three tour titles, added: "I was against such a great player. I just had to go for it, because anything can happen."
The seventh seed unleashed some powerful serves and venomous groundstrokes and chased everything the lofty American threw at her, breaking serve at 5-4 to take the first set.
Pennetta broke her opponent at 2-2 in the second and with the help of a succession of double faults and sloppy returns from Williams, opened up a comfortable 4-2 cushion.
However, the winner of 36 WTA titles came straight back, whacking a series of topspin-loaded forehands to turn the match around and move 6-5 ahead.
TENSE TIEBREAK
Pennetta levelled to force a tense tiebreak, which she clung on win 10-8, punching the air with both fists and breathing a huge sigh of relief.
"She played really well, she was eager," a sombre-looking Williams told reporters. "I made a lot of errors, a lot of mistakes. She did a good job of staying in the match.
"I wasn't surprised by her, she's capable of playing well."
The loss leaves Williams facing an anxious wait to see if she will get one of the eight spots at the season-ending championships in Madrid.
She is currently eighth in the WTA Race with the first four berths already assured.
Pennetta will meet either Zi Yan of China or Taiwan's Chan Yung-jan in Sunday's final.