STUTTGART, Germany (AP) _ Mariano Zabaleta ousted top-seeded Gaston Gaudio from the Mercedes Cup with a 6-4, 6-0 victory on Wednesday.

Neither Argentine dominated with his serve as Zabaleta broke for a 4-3 lead in the first set. He fended off three Gaudio break points to hold service and take the opening set 6-4.

Gaudio, ranked No. 14, was wiped out in second set with Zabaleta moving on to face Luis Horna of Peru in the third round. Horna defeated Spain's Albert Portas 7-6 (4), 6-2.

Third-seeded David Ferrer wasted five match points before beating Jiri Novak 6-3, 6-1 in 57 minutes.

Austria's Oliver Marach defeated 16th-seeded Richard Gasquet 6-4, 6-2; while compatriot Stefan Koubek knocked out Teimuraz Gabashvili 7-6 (6), 6-2.

Also, Switzerland's Stanislas Wawrinka topped 15th-seed Bjorn Phau 6-7 (3), 6-2, 6-3.

Another surprise came as Argentine qualifier Juan Martin Del Potro won his third ATP-level match 6-2, 4-6, 6-3 over No. 8 Juan Ignacio Chela.

The 17-year-old Del Potro led 6-2, 3-0, but Chela fought back to force a third set. Del Potro came through with three breaks in three chances in the final set.

Two more Argentinians reached the third round as Juan Monaco advanced over No. 6 Kristof Vliegen and fifth-seeded Jose Acasuso moved past Andreas Seppi. Monaco won the first set 6-3 and led 1-0 in the second when Vliegen retired with an right shoulder injury. Acasuso won 6-4, 7-6 (2).

Three Austrians advanced: Jurgen Melzer of Austria defeated Max Mirnyi of Belarus 6-3, 6-1; Oliver Marach defeated 16th-seeded Richard Gasquet 6-4, 6-2; and Stefan Koubek knocked out Teimuraz Gabashvili 7-6 (6), 6-2.

Two Germans knocked off seeded players as Florian Mayer beat No. 9 Gilles Simon, 7-6 (3), 6-2; and Simon Greul rallied to defeat 11th-seeded Mikhail Youzhny 6-7 (5), 7-5, 6-4.