PRAGUE, Czech Republic (AP) _ Slava Dosedel upset top-seeded Czech compatriot Petr Korda 6-3, 6-2 at the Czech Open Thursday, thwarting Korda's hopes of becoming No. 1 in the world.

Korda might have had a chance of wresting the No. 1 ranking from Pete Sampras, who is playing at Atlanta this week. Korda is No. 2. To earn the top spot, Korda needed to win and have Sampras lose before the semifinals at Atlanta.

The Czech Open was Korda's sixth straight unsuccessful attempt to capture the top spot, following his victory at the Australian Open in January.

In beating the last seeded player in the tournament, Dosedel, ranked 47th, needed just over an hour to reach the quarterfinals.

Playing aggressively on the baseline, Dosedel, a clay-court specialist, pushed the tired Korda deep with precise forehands. Korda struggled with his serve and trailed 4-0 after a string of unforced errors and double faults.

Korda then broke Dosedel's serve, rallying to 3-4, but failed to convert several key shots and eventually lost the set.

Dosedel, winner of three ATP tournaments during his nine-year career, broke Korda again in the fourth and eighth games of the second set, reaching his first quarterfinal this year.

Korda called the match one of the worst of his career.

In other marches, Nicolas Lapenti of Ecuador defeated Germany's Martin Sinner 6-2, 6-0; Spain's Fernando Vicente beat Renzo Furlan of Italy 3-6, 6-1, 6-4, and Jacobo Diaz of Spain beat Austria's Gilbert Schaller 4-6, 6-1, 6-4.