NEW YORK (AP) — Serena Williams needed just 49 minutes to advance a day after her sister withdrew at the U.S. Open.

The 13-time Grand Slam champion beat 183rd-ranked Dutch qualifier Michaella Krajicek 6-0, 6-1 in the second round Thursday. She closed it out with her 10th ace.

On Wednesday, Venus Williams revealed that she had been diagnosed with an autoimmune disease that causes fatigue and joint pain. Younger sister Serena is coming off her own health scare of blood clots in her lungs over the winter. But she won two tournaments heading into the Open and is considered a favorite in the wide-open women’s field despite being seeded 28th.

Williams had 25 winners and just 10 unforced errors. She could face fourth-seeded Victoria Azarenka in the third round.

Krajicek, the younger sister of 1996 Wimbledon champion Richard Krajicek, was playing in her first major tournament since 2008.

Copyright 2011 The Associated Press.

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