Britons Heather Watson and Katie Boulter fell to straight-set defeats in the first round at Indian Wells.
World number 113 Watson, 29, battled early in set one but failed to take two break points at 2-2 and Czech Tereza Martincova pushed on to a 6-2 6-1 win.
Boulter, 25, was broken three times in her opening set against Italy's Jasmine Paolini and lost 6-3 6-2.
British interest in the tournament rests on Heather Dart and Emma Raducanu, who are both into round two.
However, British qualifiers Watson and Boulter both struggled to gain a footing in testing contests played out in blustery conditions in California.