Serena Williams' Indian Wells Open campaign ended in retirement after the 23-time grand-slam winner complained of a left-leg injury midway through her match with Garbine Muguruza.
Williams made a solid start to Sunday's contest in California as she raced into a 3-0 lead, the 10th seed dominating from the baseline with a string of powerful forehands.
However, the 37-year-old was was not moving freely and Muguruza battled back with a series of stunning groundstrokes of her own.
Muguruza reeled off six successive games to take the first set but Williams' mobility was well short of her best, and her retirement seemed inevitable at the changeover.
Having called for the trainer, Williams complained of a pain in her left leg but tried to battle on at the start of the second set.
Muguruza held to love with Williams not even trying to run for the game-winning point and on her return to the chair the American was noticeably breathing heavily.
She quickly called time on proceedings, handing Muguruza a place in the last 16 –the match ended 6-3, 1-0– where she will meet Kiki Bertens or Johanna Konta.
During the interview at the end of the match, Muguruza wished Serena a quick recovery; "I wish I am going to see her very soon and better!"