BANGKOK, Sept 30: World number one Roger Federer led the top four seeds into the quarter-finals of the Thailand Open by defeating Swiss compatriot Ivo Heuberger 6-1 6-3 on Thursday.

Second seed Andy Roddick was handed a stern test before he overcame his friend and fellow American Jeff Morrison 6-2 6-7 6-4 while Marat Safin and Thailand's Paradorn Srichaphan reached the last eight with straight set victories.

Federer, winner of three grand slam titles this year, took the first set in just 20 minutes after breaking for a 2-1 lead. The top seed built a 5-1 cushion in the second set before giving up his serve with a double fault despite holding three match points. But he finally clinched the contest with his sixth ace.

Roddick turned his thoughts to the United States' Davis Cup final against Spain in December after his victory over Morrison. Russian third seed Safin also needed several match points to beat Jiri Vanek of the Czech Republic 6-3 6-4.

Local favourite and fourth seed Paradorn edged out American Alex Bogomolov Jr 6-0 7-6 to keep the home fans happy. Last year's champion, Taylor Dent of the United States was beaten 6-0 6-4 by Dutchman Dennis Van Scheppingen.

RESULTS: Andy Roddick (U.S.) bt Jeff Morrison (U.S.) 6-2 6-7 (4-7) 6-4; Paradorn Srichaphan (Thailand) bt Alex Bogomolov Jnr (U.S.) 6-0 7-6 (7-4); Roger Federer (Switzerland) bt Ivo Heuberger (Switzerland) 6-1 6-3; Marat Safin (Russia) bt Jiri Vanek (Czech Republic) 6-3 6-4; Dennis van Scheppingen (Netherlands) bt Taylor Dent (U.S.) 6-0 6-4; Robin Soderling (Sweden) bt Paul Baccanello (Australia) 6-1 6-3; Flavio Saretta (Brazil) bt Rogier Wassen (Netherlands) 3-6 6-1 6-2; Thomas Johansson (Sweden) bt Adrian Garcia (Chile) 6-3 6-3.