Serena Williams of the United States returns a shot against Alexa Glatch of the United States during day one of the 2009 U.S. (Al Bello/Getty Images)
The world number two, looking for her third grand-slam title of the year and 12th in all, survived a lapse in concentration midway through the first set to advance in just over an hour.
Williams began strongly but was broken when serving for the opening set at 5-2 as world number 103 Glatch settled after a nervous start.
But she made no mistake second time round and then cruised through the second to set up a clash with Italian Maria Elena Camerin or Hungary's Melinda Czink.
