Pegula into Miami semis as Badosa
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Pegula, whose parents are the principal owners of the Buffalo Bills NFL franchise, was leading 4-1 when fifth seed Badosa called the trainer.
After a brief discussion, it was decided the Spaniard was unable to carry on.
"It's not nice to win like that, I was looking forward to playing her, she has had an amazing year," 16th seed Pegula said afterwards.
"But she wasn't looking well, hopefully we can play again when she is healthy," the American added.
Pegula will face either world number one Iga Swiatek or Petra Kvitova in the last four.