Belinda Bencic upset world number three Coco Gauff on Wednesday to line up a quarter-final clash with Australian Open champion Madison Keys at Indian Wells.
Switzerland's Bencic triumphed 3-6, 6-3, 6-4 to reach her first WTA 1000 quarter-final since becoming a mother last year.
Keys also had to rally, downing Croatia's Donna Vekic 4-6, 7-6 (9/7), 6-3 to advance in her first tournament since she captured her maiden major in Melbourne.
Bencic dominated after dropping the first set to avenge a fourth-round loss to Gauff at the Australian Open this year.
The 28-year-old former world number four didn't face a break point after the opening set and kept the pressure on Gauff, who struggled with her forehand after her aggressive start to the game.
It was a loose forehand return which handed Bencic the crucial second break point at 4-4 in the third set and she confidently served out to clinch victory.
Bencic, who gave birth to daughter Bella last April, was unranked when she returned to action in October. But she has gone from strength to strength, claiming her ninth career title in Abu Dhabi last month to rise to 58th in the world this week.
She said her improved fitness was a factor in her ability to best Gauff in three sets this time, when she couldn't in Melbourne in January.
"What changed is that I just kept on working also on the physical side," Bencic said.
"I felt like in the last matches in tournaments, I kind of was able to play back to back, some three-set matches, and am fresher every time.
"The body is holding up much better, almost like it was before."
Keys unleashed a barrage of winners to vanquish Vekic, but after dropping the opening set and failing to convert a set point in the 10th game of the second the American had to gut out a tense second-set tiebreaker in which Vekic moved within two points of victory when she led 5-3.
Keys broke Vekic in the opening game of the third to give herself some breathing room and broke her again to lead 5-2. Vekic managed to pull back one break but Keys gave herself double match point with a blistering backhand service return in the next game and sealed the victory on her second opportunity.
- Alcaraz in action -
Two-time defending champion Carlos Alcaraz headlines the night session on Stadium Court as he continues his bid to join Roger Federer and Novak Djokovic as the only men to win three straight Indian Wells titles.
The world number three from Spain faces Bulgarian veteran Grigor Dimitrov, who beat Alcaraz in their last two meetings, including a straight-sets win in Miami last year.
The winner of that match will face Argentina's Francisco Cerundolo, who beat world number 10 Alex de Minaur of Australia 7-5, 6-3.
Women's world number one Aryna Sabalenka of Belarus eased into the quarter-finals with a 6-1, 6-2 victory over British lucky loser Sonay Kartal.
Sabalenka will next face either world number six Jasmine Paolini of Italy or Russian Liudmila Samsonova.
American Ben Shelton triumphed in his all-American clash with compatriot Brandon Nakashima 7-6 (8/6), 6-1 to advance to his third ATP Masters 1000 quarter-final.
Shelton, 22, becomes the youngest American man in the last eight at Indian Wells since Andy Roddick in 2004.
Shelton was two points away from losing the first set when he was 6-6 in the tie-break, but Nakashima missed a backhand volley and then found the net.
From then on it was all Shelton.
"For me the second set was outstanding. Whenever you can get a two-break win in a set against a server like him is really encouraging for where my level is at," Shelton said.
He will face either 2022 champion Taylor Fritz, seeded third, or Britain's Jack Draper for a place in the semi-finals.
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