World number two Aryna Sabalenka fell to a surprise defeat by Emma Navarro in the fourth round of Indian Wells.
Belarusian Sabalenka, who successfully defended her Australian Open title in January, lost 6-3 3-6 6-2 to the 23rd seed.
Navarro was cheered on by the California crowd as she reached her first WTA 1000 quarter-final.
Fellow American and third seed Coco Gauff claimed a 6-0 6-2 win over Belgium's Elise Mertens.
Playing on her 20th birthday, 2023 US Open champion Gauff wrapped up the first set in 25 minutes.
Mertens finally got on the board with a break and held serve to level the second set at 2-2, but Gauff regained control and won four games in a row to reach the last eight for a second straight year.