TENNIS: US OPENDefending champion Novak Djokovic of Serbia sailed into the quarter-finals of the US Open yesterday when fourth-round opponent Stanislas Wawrinka of Switzerland retired hurt.

Djokovic was in control, leading 6-4 6-1 3-1 after an hour and a half on the Louis Armstrong Stadium court, when Wawrinka quit after getting medical help from his trainer at the change of ends.

Djokovic, who won the US Open for the first time last year, will play American Andy Roddick or Argentine Juan Martin del Potro in today’s quarter-finals. The world number two has not dropped a single set in the tournament so far.

Serbia’s Janko Tipsarevic successfully wore down Germany’s Philipp Kohlschreiber to win their rain-delayed fourth-round clash 6-3 7-6 6-2. Kohlschreiber blasted 12 aces during the two and a half hour clash that began on Tuesday but was suspended for a day because of rain. Tipsarevic’s quarter-final opponent is Spanish fourth seed David Ferrer, who beat the foul weather to win his match on Tuesday and get a day off.