Britain's Emma Raducanu lost her first match as a Grand Slam champion, beaten in straight sets by Belarus' Aliaksandra Sasnovich at Indian Wells.
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 Britain was competing in Indian Wells without a permanent coach having ended her partnership with Andrew Richardson, whom she has known since the age of 10.
Speaking after the match, she said: "We had some great memories together - at the US Open and also previous to that - but I'm looking forward to the next chapter and I think that what I am doing right now is definitely the best for me and my tennis.