The top-ranked Swiss player had 17 aces, but also many unforced errors, against the 80th-ranked Belgian. It was Federer's first match since he started working with coach Jose Higueras, a clay-court specialist.
Federer is struggling through his worst start to a season since 2000 -- the last time he went four tournaments without a victory. Only two Grand Slam titles short of tying Pete Sampras' record of 14, Federer still needs to win the French Open to complete a career Grand Slam.
Second-seeded Nikolay Davydenko also made a shaky start against Jurgen Melzer but recovered to win 6-3, 6-1. Davydenko, coming off a victory at the Sony Ericsson Open, lost his first service game and trailed 2-0 before breaking his opponent's serve three times in the first set.
The Russian won the Estoril Open title in 2003 and lost in the final two years ago.