Reigning champion and two-time runner-up Novak Djokovic was an easy fourth-round winner Wednesday at the U.S. Open.

The second-seeded recent world No. 1 star won his 11th straight match in Flushing with a 6-4, 6-1, 3-1 spanking of 18th-seeded Swiss Stanislas Wawrinka, who appeared ill and decided to retire in the third set. The match was suspended by rain on Tuesday night, with the formidable Serb leading 2-0 in the first set. Rain also interrupted play here on Wednesday.

Djokovic dismissed Wawrinka in 1 hour, 33 minutes.

The 25-year-old Serb will meet the Juan Martin del Potro-Andy Roddick winner in a quarterfinal on Thursday. Del Potro and Roddick are both former U.S. Open champs.

The five-time Grand Slam champion Djokovic captured his first U.S. Open title last year by handling former winner Rafael Nadal in a 1-versus-2 finale at the National Tennis Center. The Serb also stopped the Spaniard in this year's epic Australian Open finale, while Nadal beat Djokovic in the French Open final in June.

Also on Day 10 in New York, Djokovic's eighth-seeded fellow Serb Janko Tipsarevic dismissed 19th-seeded German Philipp Kohlschreiber 6-3, 7-6 (7-5), 6-2 to reach the U.S. Open round of eight for a second straight year. Tipsarevic-Kohlschreiber was also suspended because of rain on Tuesday, with the Serb leading 5-2 in the opening set.

Tipsarevic is rewarded with a quarterfinal match against fourth-seeded fellow grinder David Ferrer of Spain.