COSTA DO SAUIPE, Brazil -- American Cecil Mamiit upset U.S. Open semifinalist Sjeng Schalken of the Netherlands 6-3, 7-6 (6) on Wednesday in the second round of the Brazil Open.

"I didn't expect this victory,'' said the 128th-ranked Mamiit, who wore a U.S. flag pin on his shirt in memory of the victims of the terrorist attacks. "I kept winning points and gaining confidence as the match went on.''

The American had eight aces to just one for the second-seeded Schalken, ranked 17th.

In other second-round matches, seventh-seeded Dominik Hrbaty of Slovakia beat American Brian Vahaly 4-6, 6-2, 6-2, and fifth-seeded Agustin Calleri of Argentina defeated American Vince Spadea 7-6 (1), 7-5.

In women's play, second-seeded Monica Seles advanced to the quarterfinals with a 7-5, 6-1 victory over Slovenia's Tina Pisnik in a match interrupted by rain.

"Pisnik was playing well at the start and I took a while to get into the match,'' Seles said. "It was a good debut.''

Seles will face Henrieta Nagyova of Slovakia, who upset fifth-seeded Iva Majoli of Croatia 6-2, 6-3.

Also, top-seeded Jelena Dokic of Yugoslavia beat Myriam Casanova of Switzerland 7-6, 6-4, and third-seeded Anastasia Myskina of Russia defeated American

Also, top-seeded Jelena Dokic of Yugoslavia beat Myriam Casanova of Switzerland 7-6, 6-4, and third-seeded Anastasia Myskina of Russia defeated American Sunitha Rao 6-2, 6-2.

In other second-round matches, South Africa's Amanda Coetzer beat seventh-seeded Nathalie Dechy of France 6-2, 3-6, 6-3, and eighth-seeded Eleni Danilidou of Greece beat France's Emilie Loit 4-6, 6-2, 7-5.