Raonic, the No. 5 seed from Thornhill, Ont., served 19 aces in the straight-set victory over the German, who made it to the final of the 2011 event. Raonic will next play Ze Zhang of China, who overcame another German, Tobias Kamke, 6-4, 7-6 (2).
Philipp Kohlschreiber began his title defence at the grass-court tournament with a win over wild card Dustin Brown in an all-German matchup.
The 163rd-ranked Brown twice pushed Kohlschreiber to a tiebreak, before the eighth-seeded defending champion won 7-6 (4), 7-6 (4) in one hour 23 minutes.
The 28-year-old Kohlschreiber will face Lukas Kubot after the Pole beat Jarkko Nieminen of Finland 6-4, 6-4.
Kohlschreiber was relieved to see off Brown's challenge — Brown served two aces in succession to take the second set to the tiebreaker — and admitted that nerves had played a role.
"Then I struck the ball very well and I can also be happy with my return," Kohlschreiber said.
In other matches, Mikhail Youzhny of Russia beat Dutchman Robin Haase 6-3, 6-2 and Germany's Cedrik-Marcel Stebe beat Argentina's Carlos Berlocq 6-3, 3-6, 7-5.
Rafael Nadal, who won his record seventh French Open title earlier Monday, and five-time winner Roger Federer both have byes to the second round.
Federer has been honoured by having a street leading to the stadium in Halle named after him when the Roger Federer Allee was officially inaugurated Monday afternoon.
"Now I will practically always be here," Federer said.
The 16-time Grand Slam winner called the gesture an "unbelievably big honour."