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.