Halle - Philipp Kohlschreiber began the defence of his Gerry Weber Open title with a win over wildcard Dustin Brown in an all-German match-up on Monday.
The 163rd-ranked Brown twice pushed Kohlschreiber to a tie-break, before the eighth-seeded defending champion won 7-6 (7/4), 7-6 (7/4) 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 (7/1), setting up a second round clash with Ze Zhang of China, who overcame another German, Tobias Kamke, 6-4, 7-6 (7/2).
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 tie-breaker - 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 on 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 on Monday afternoon.
"Now I will practically always be here," Federer said.
The 16-time Grand Slam winner called the gesture an "unbelievably big honour."
Results on Monday from the opening day of the Gerry Weber Open on grass at Gerry Weber Stadion (seedings in parentheses):Singles
Mikhail Youzhny, Russia, def. Robin Haase, Netherlands, 6-3, 6-2.
Cedrik-Marcel Stebe, Germany, def. Carlos Berlocq, Argentina, 6-3, 3-6, 7-5.
Ze Zhang, China, def. Tobias Kamke, Germany, 6-4, 7-6 (2).
Lukas Kubot, Poland, def. Jarkko Nieminen, Finland, 6-4, 6-4.
Philipp Kohlschreiber (8), Germany, def. Dustin Brown, Germany, 7-6 (7/4), 7-6 (7/4).
Milos Raonic (5), Canada, def. Philipp Petzschner, Germany, 7-5, 7-6 (7/1).
Johan Brunstrom, Sweden and Philipp Marx, Germany, def. Tommy Haas, Germany and Alexander Waske, Germany, 6-4, 6-2.