GSTAAD, Switzerland -- French Open champion Albert Costa was upset by qualifier Paul Henri Mathieu in straight sets Tuesday in the opening round of the Swiss Open.

Frenchman Mathieu, who went through two rounds of qualifying, beat the top-seeded Spaniard 6-4, 6-3 in Costa's first match since defeating compatriot Juan Carlos Ferrero last month in Paris.

This $600,000 tournament is a favorite of Costa, a winner here in 1996 and 1999.

In other first-round play, Attila Savolt of Hungary upset sixth-seeded Nicolas Lapentti of Ecuador 7-5, 1-6, 7-5.

Still seeking his first title on home clay, third-seeded Roger Federer kept organizers happy, beating Hicham Arazi of Morocco 6-4, 6-3. The defeat came as a surprise to Lapentti, a clay-court specialist who reached the quarterfinals at Wimbledon.

Lapentti reached the final here in 1999 before losing to Costa. Federer lost to Arazi in straight sets two months ago at the French Open.

In other first-round play, seventh-seeded Gaston Gaudio of Argentina defeated compatriot Franco Squillari 2-6, 6-1, 6-4.

Also ousted was George Bastl of Switzerland, who made headlines by eliminating Pete Sampras in the second round at Wimbledon. Compatriot and fellow wild card Marc Rosset beat Bastl 7-6 (5), 3-6, 6-3.

Surprise Wimbledon finalist David Nalbandian of Argentina was supposed to go back to work following his stunning performance last week in England, but his match with fourth-seeded Andrei Pavel of Romania was rained out.