Kim Clijsters ended Martina Hingis' comeback at the Australian Open with a battling 6-3 2-6 6-4 win to set up a semi-final with Amelie Mauresmo.
The second seed quickly went 4-0 up and although Hingis broke back, Clijsters' fierce strokes saw her seal the opener.
Former champion Hingis slid 2-0 down in the second but dug deep to break Clijsters twice and level the contest.
The players traded breaks in a tense decider, but Clijsters' power proved decisive and she served out the match.
The Belgian 22-year-old seemed to be on her way to a comfortable win as she broke Hingis to love in the first game.
After taking the first set, she had Hingis on the rack at 0-2 and 0-40 down in the second.
But Hingis refused to cave in and clawed back all three break points before going on to break Clijsters in the next game.
"She's definitely improved a lot, even compared to when she was at her best"
The 25-year-old used all her subtlety to bamboozle the second seed with an array of shots while Clijsters lost her focus, making a host of unforced errors as Hingis broke her again to force the decider.
Clijsters responded by breaking Hingis in her first service game for the third set in a row.
The Swiss again rose to the challenge and broke back but this time Clijsters did not waver and immediately claimed a second break at 4-3 before serving out the match.
Clijsters was full of praise for Hingis, who was playing her first Grand Slam tournament in four years as a result of long-term injury problems.
"She's definitely improved a lot, even compared to when she was at her best," said Clijsters, who will now take over the world number one ranking form Lindsay Davenport.
"I think I can be proud of myself - I just have to work harder "
"After the year I had last year, this is the cherry on the cake, it just tops it off," added Clijsters, who has had major injury problems of her own.
Hingis was upbeat despite her defeat, saying: "I think I can be proud of myself - you just can't think you're going to go out there and win everything.
"Losing to Kim still gives me so much to look forward to. I just have to work harder. I have to start believing."
Mauresmo breezed into the Australian Open semi-finals with an easy 6-3 6-0 win over Patty Schnyder.
It was a totally one-sided affair at Melbourne Park as the Swiss seventh seed, despite loud support from the crowd, offered little resistance.
The players exchanged breaks in the opener but the third seed broke Schnyder at 4-3 and won the next eight games to wrap up victory.
"That's what I wanted, from the first point really making her play as much as I could," said Mauresmo.
"I did that very well at the beginning and felt my game was very effective."
Schnyder admitted she had no answers to Mauresmo's all-round display.
"I think it's really one of the rare ones where there was no match at all. I was just off, and she was all over me.
"I don't know really what happened to me. She just took advantage and didn't let it go."