Defending champion Olivier Rochus lost 6-2, 6-4 to eighth-seeded Jurgen Melzer of Austria in the first round of the BMW Open on Monday.
"I didn't have a good day," Rochus said after his quick defeat.
The Belgian struggled with Melzer's serve, with the Austrian firing seven aces and winning 81 percent of his first-serve points.
Melzer broke Rochus' serve twice in the first set, before falling behind 3-0 in the second. But Melzer then won five straight games to gain the upper hand and avenge his semifinal loss last year to Rochus.
Third-seeded Mikhail Youzhny and No. 4 Marcos Baghdatis also advanced to the second round of the euro353,450 (US$416,000) clay-court tournament.
Youzhny defeated Stefan Koubek 6-4, 3-6, 6-1 and Baghdatis beat Diego Hartfield 7-6 (5), 6-3.
Philipp Kohlschreiber beat Arnaud Clement 6-2, 7-6 (5).
Kohlschreiber led 5-4 and served for the match but dropped his serve to extend the match.