Mikhail Youzhny opened his BMW Open title defense on Monday with a 7-5, 6-2 victory over German wild card Matthias Bachinger.
Youzhny is seeded first at the tournament, where he also was twice runner-up.
In other first-round matches, fourth-seeded Marcos Baghdatis defeated Julien Benneteau 7-6 (2), 6-3; sixth-seeded Sergiy Stakhovsky advanced when Denis Istomin quit while trailing 5-1; and Horacio Zeballos defeated Robert Kendrick 6-4, 6-4.
Tommy Haas, once ranked No. 2, was to make his comeback in a doubles match. He had been out 14 months with various injuries. Haas had surgery on his right hip in February last year and on his right elbow a month later.
The 33-year-old German will not play singles and will partner Radek Stepanek in doubles.
"I'm looking forward to the tests of seeing how my body feels, playing competitively again," Haas said. "Going out there is something you can't really practice, so being tight and kind of nervous, and wanting to win again, I need to see how that feels and also see how my body responds.
"I'm hoping to see what it's like, and hopefully make a return in singles the next few weeks."