The top-seeded Hingis, playing a third-round match, struggled early before eliminating American Corina Morariu, 7-5, 6-2, and No. 3 Pierce of France knocked off American Chanda Rubin, 6-1, 6-2.

Pierce lost to Hingis in the final of the Porsche Tennis Grand Prix in Filderstadt, Germany on Sunday.

As for the second-seeded Williams, she renewed her rivalry with Irina Spirlea of Romania and cruised to a 6-3, 6-2 win in a second-round match. The two engaged in an infamous bumping incident during a changeover in their U.S. Open semifinal match two years ago.

Williams did not play last week after losing to younger sister Serena in the final of the Grand Slam Cup in Munich the week before.

The 19-year-old Williams is 36-8 on hard courts this season, winning two titles on the surface. She reached the final here last year but lost to Lindsay Davenport.

Wednesday, fourth seed Amanda Coetzer of South Africa battled her way into the quarterfinals, by rallying past local favorite Patty Schnyder of Switzerland, 1-6, 6-3, 6-2.

First prize is $150,000.