New York ? Venus Williams pulled out of the U.S. Open shortly before her second-round match Wednesday, saying she was diagnosed with Sjogren’s Syndrome, an autoimmune disease that causes fatigue and joint pain.

The 31-year-old American, the champion at Flushing Meadows in 2000 and 2001, played her first match in two months Monday, when she beat Vesna Dolonts 6-4, 6-3 in the first round. Williams was supposed to face 22nd-seeded Sabine Lisicki on Wednesday.

Lately, as Williams and 29-year-old sister Serena have dealt with health problems and played less frequently, people have wondered when — and perhaps whether — another American woman would make an impact in the sport. For one day, at least, Christina McHale and Irina Falconi did just that.

McHale, a 19-year-old from Englewood Cliffs, N.J., delivered a 7-6 (2), 6-2 victory over eighth-seeded Marion Bartoli of France, the runner-up to Venus Williams at Wimbledon in 2007. Falconi, a 21-year-old who went to Georgia Tech, followed that up by beating 14th-seeded Dominika Cibulkova of Slovakia 2-6, 6-3, 7-5.

On Wednesday night, Andy Roddick, the 2003 U.S. Open champion, held on to beat 96th-ranked Michael Russell 6-2, 6-4, 4-6, 7-5 in all-American first-round match. Enduring a rough season filled with injuries, No. 21 Roddick dropped out of the top 20 in the rankings for the first time in 10 years.

After his victory, 2006 U.S. Open champion Maria Sharapova beat 84th-ranked Anastasia Yakimova of Belarus 6-1, 6-1 in a match that ended a little past midnight.