By Steve Keating
NEW YORK (Reuters) - Juan Martin del Potro's summer renaissance continued on Monday as the unseeded Argentine advanced into the U.S. Open quarter-finals when Austrian eighth seed Dominic Thiem quit their match with an injury.
Del Potro, the 2009 U.S. Open winner, whose career has been interrupted by a string of wrist surgeries and needed a wild card to get into the year's last grand slam, has made the most of his opportunity by reaching the last eight without dropping a set.
The towering Argentine's path was made a little easier when Thiem retired with an apparent knee injury trailing 6-3 3-2.
Del Potro will now await the winner between third seed Swiss Stan Wawrinka and Ukraine's Illya Marchenko.
(Editing by Frank Pingue)