World number two Aryna Sabalenka fell to a surprise defeat by American Emma Navarro in the fourth round of Indian Wells.
Sabalenka, who successfully defended her Australian Open title in January, lost 6-3 3-6 6-2 to the 23rd seed.
The home hope was cheered on by the California crowd as she reached her first WTA 1000 quarter-final.
Navarro will face Greek ninth seed Maria Sakkari or France's Diane Parry on Thursday.
Navarro broke in the eighth game for the chance to serve out the first set, but she was forced to save a break-back point against the Belarusian before taking the opener.