World number one Naomi Osaka's defence of her Indian Wells title was ended in round four by Belinda Bencic.
Japan's Osaka, who holds the US Open and Australian Open titles, was beaten 6-3 6-1 by the Swiss world number 23 in just over an hour.
World number two Simona Halep of Romania is also out, beaten 6-2 3-6 6-2 by Czech teenager Marketa Vondrousova.
It was a first win over a top-five player for the 19 year old, who is ranked 61st in the world.
Halep's defeat in California means 21-year-old Osaka, who claimed her first WTA title with victory at Indian Wells last year, will keep her number one ranking, despite losing to 22-year-old Bencic.
"I didn't play that well," Osaka said. "Honestly, at a time like this with that scoreline, I would usually feel very depressed and sad.
"But I feel pretty good right now because I tried my best and I don't really have any regrets.
"She was just playing so well. There wasn't anything that I could do in that situation."
Bencic, who beat four top-10 players on the way winning a title in Dubai last month, faces world number five Karolina Pliskova, who beat Anett Kontaveit 7-6 (7-0) 4-6 6-2, in the quarter-finals.
"I'm very confident with my game right now. I'm hitting the ball well. So just things worked out for me," said Bencic.
Vondrousova had defeated 2017 French Open champion Jelena Ostapenko and last year's Indian Wells finalist Daria Kasatkina prior to beating Halep.
"I was running a lot - I felt like I was dying for a moment," Vondrousova joked in an on-court interview.
"I'm so happy to be through and so happy with my play."
She will play Ukraine's Elina Svitolina, who beat Australian Ashleigh Barty 7-6 (10-8) 5-7 6-4, in the next round.
Vondrousova served for the match at 5-1 in the third set but was broken to 15, before breaking back in a scrappy game from Halep to seal the win.
French Open champion Halep, who is still without a permanent coach, has not won a WTA title since the Canadian Open in August.
Canada's Bianca Andreescu, 18, continued her remarkable season with a 7-5 6-2 win over China's Wang Qiang.
Andreescu, who beat Caroline Wozniacki and Venus Williams on her way to the Auckland Open final in January, has won 23 and lost just three matches this year.
She will play Spain's Garbine Muguruza next, after the former world number one beat Kiki Bertens 5-7 6-1 6-4.