Former world number one Maria Sharapova fell 6-4 6-4 against Japanese number one Naomi Osaka in the first round at Indian Wells.
It is a second opening round loss in succession for the 30-year-old after she was knocked out of the Qatar Open last month.
Sharapova made six double faults, won only 25% of her second-serve points and had her serve broken five times.
Osaka, 20, the world number 44, wrapped up victory in 95 minutes.
“I wanted to do well here and not just because I won this event a couple times,” said Sharapova, who won the Indian Wells title in 2006 and 2013 but was unseeded for this year’s event, having dropped to 41 in the rankings.
“I would have loved to stay longer it is just not going to happen this year.”
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In the only night session match of the day, Osaka, who beat defending champion Angelique Kerber in the first round of last year’s US Open built a 3-0 lead in the first set.
Sharapova, who returned to the tour in April last year after a 15-month doping ban, fought back to 4-4 but then a double fault handed Osaka a set point which she took.
Osaka was 4-2 up in the next set before Sharapova recovered to 4-4 once more, only for another double fault at 4-5 to hand her opponent match point.
The Japanese player will face Polish world number 31 Agnieszka Radwanska in round two.
Sharapova reached the semi-finals of the Shenzhen Open in January and round three of the year’s first Grand Slam, the Australian Open, but lost in the opening round in Doha last month.
BBC tennis correspondent Russell Fuller
Aside from winning her 36th career title in Tianjin in October, life has been a struggle for Sharapova since she returned from a doping ban last April.
A left arm problem is the latest in a succession of injuries which have held her back, and her lack of fluency was all too apparent against the powerful 20-year-old Osaka on a chilly night in Indian Wells.
Sharapova’s last win came in the second round of the Australian Open in January, and she remains outside the world’s top 40 – 10 months after returning to the tour.