Elena Rybakina and Jessica Pegula both pulled of Australian Open quarter-final upsets, knocking out higher seeds Iga Swiatek and Amanda Anisimova respectively.
Second seed Swiatek, who has never won the Australian Open title - the only Grand Slam she has left to lift - was defeated 7-5 6-1 by sixth seed Rybakina as the latter took advantage of an error-filled effort by Swiatek.
The 24-year-old Pole committed 25 unforced errors while hitting just 10 winners. Rybakina, 26, had a steadier ground game with 25 winners and 19 unforced errors.
"I'm really pleased with the win," Rybakina said in her on-court interview. "We know each other pretty well, and I was just trying to stay aggressive.
"In the first set, the first serve wasn't working for both of us, so we were trying to step in on the second serve and put pressure on each other.
"In the second set, I just started to play more free, serve better, and I'm really happy with the win."
Rybakina is through to a major semi-final for the first time since she reached the Wimbledon semi-finals in 2024. She has made two career Grand Slam finals, prevailing at Wimbledon in 2022 and losing the Australian Open title match in 2023.
After Swiatek and Rybakina exchanged service breaks in the opening two games, Rybakina saved three break points at 1-1, then broke serve in the 12th game to take the set.
Rybakina won the first three games of the second set and cruised to the finish, never facing a break point in the set.
Sixth seed Pegula, meanwhile, stunned fellow American and two-time Grand Slam finalist Anisimova - the fourth seed - to clinch her place in the semi-finals.
The 31-year-old Buffalo native made history while beating Anisimova 6-2 7-6 (7-1), becoming the first woman in the Open Era (since 1968) to reach her first three major semi-finals after turning 30.
After Pegula cruised through the first set against 24-year-old Anisimova, neither player broke serve through the first seven games of the second set.
Anisimova got the break to go up 5-3, but she couldn't serve out the set as Pegula broke back. After another break by Pegula for a 6-5 edge, Anisimova responded in kind to force a tiebreaker.
Anisimova won the opening point of the tiebreaker before Pegula reeled off seven straight points to advance.
Pegula said: "I was like, 'It's got to be coming, you know. The next round, I've got to get to the semi,' because I feel like I play some really good tennis here and I like the conditions.
"And I've always felt like, even matches I've lost here, that I've played well. So I've been waiting for the time where I could kind of break through."
Pegula and Rybakina have split six career matches, with the Kazakhstani player having taken their latest clash in WTA Finals last fall.
A win by Pegula on Thursday would send her to her second career major final.
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