Britain’s Emma Raducanu lost her first match as a Grand Slam champion, beaten in straight sets by Belarus’ Aliaksandra Sasnovich at Indian Wells.
World number 22 Raducanu was seeking an 11th successive victory, having won the US Open last month as a qualifier.
But Sasnovich, ranked 100th in the world, beat the 18-year-old 6-2 6-4 in round two of the BNP Paribas Open.
Raducanu, who received a first-round bye, is next scheduled to play at the Kremlin Cup in Moscow in 10 days’ time.
The British number one made an excellent start – holding to love in the opening game of the match in front of a supportive crowd of about 4,000 for the night session.
But a loose service game followed, and with Sasnovich, 27, playing some excellent defensive tennis, the US Open champion was forced in to too many errors.
Raducanu seemed anxious to close out rallies quickly on the slow court, and Sasnovich broke again to love and took the opening set.
It was the first set Raducanu had lost since a three-set defeat to Clara Tauson in the final of the Challenger event in Chicago on 22 August.
Sasnovich broke first in the second set too, as she showed off the attacking side of her game.
But two double faults followed in the next game and with Raducanu beginning to find some composure, the teenager was able to open a 4-2 lead.
The improvement was short-lived, however, and Sasnovich won the final four games of the match to complete a straight-set victory.
The Belarusian will play two-time Grand Slam champion Simona Halep in the third round on Sunday.