Philipp Kohlschreiber began the defense of his Gerry Weber Open title with a win over wild card Dustin Brown in an all-German matchup on Monday.
The 163rd-ranked Brown twice pushed Kohlschreiber to a tiebreak, before the eighth-seeded defending champion won 7-6 (4), 7-6 (4) in 1 hour, 23 minutes.
Canada's Milos Raonic, the other seeded player playing on the opening day of the grass-court tournament, defeated last year's beaten finalist, Philipp Petzschner.
Fifth-seeded Raonic served 19 aces to beat the German 7-5, 7-6 (1), setting up a second round clash with Ze Zhang of China, who overcame another German, Tobias Kamke, 6-4, 7-6 (2).
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.
There were wins too for Mikhail Youzhny of Russia, who beat Dutchman Robin Haase 6-3, 6-2, and Germany's Cedrik-Marcel Stebe, who defeated 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 honored 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 honor.''
