Top-ranked Serena Williams outlasted Anabel Medina Garrigues 6-3, 0-6, 7-5 to reach the Madrid Open semifinals on Friday.
Williams appeared to wear down against the scrappy Spaniard on the red clay court, and after getting blanked in the second set she fell behind 4-2 in the decider.
But the defending champion rallied back to break Medina Garrigues' serve twice to move on.
''It was definitely a battle,'' Williams said. ''I obviously didn't do much in the second set and gave her confidence to play better.''
Williams will next face either Sara Errani or Ekaterina Makarova.
Second-seeded Maria Sharapova had less trouble easing by Kaia Kanepi of Estonia 6-2, 6-4 to set up a semifinal with either fellow former No. 1 Ana Ivanovic or Angelique Kerber.
Williams' entertaining match at the Caja Magica against an opponent she had rightly described as a ''grinder'' the day before took several momentum swings.
The 63rd-ranked Medina Garrigues has 10 career clay-court titles - the most of ...