Stanislas Wawrinka (back) retires
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The second-seeded Wawrinka stopped after a medical timeout more than 2 hours into his match with Feliciano Lopez, who was leading 6-4, 2-6, 4-3.
The 10th-ranked Wawrinka has won only five matches -- all against players outside the top 50 -- in seven visits since reaching the 2005 final of his home tournament.
The sixth-seeded Russian saved three match points in the tiebreaker.
Copyright 2013 by The Associated Press
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