PHILADELPHIA -- Top-seeded Monica Seles advanced easily, but No. 2 Gabriela Sabatini had trouble before moving into the quarterfinals.
Also struggling to win was fourth-seeded Jennifer Capriati, who outlasted Lori McNeil in a marathon match.
Seles started slowly but rallied to beat Marianne Werdel, 7-5, 6-1.
Sabatini, ranked No. 3 in the world, squandered five service breaks before settling down to post a 7-6 (7-5), 2-6, 6-2 victory and improve to 7-0 in her career against Natalia Zvereva, who is ranked 19th.
Capriati, No. 6 in the world rankings, needed 2 hours, 17 minutes to edge No. 20 McNeil, 7-6 (11-9), 6-7 (4-7), 6-2.
No. 6 Conchita Martinez topped Helena Sukova, 6-3, 6-2.
Va. Slims of Philadelphia