(Reuters) - Roger Federer began his bid for a ninth Gerry Weber Open title with a 6-4 7-6(3) first round win over German wildcard Jan-Lennard Struff on Wednesday.
The Swiss top seed, still without a title during an injury-hampered 2016 season, kept his cool during a contest which featured only one break of serve.
Federer, who missed the French Open due to a back problem, fired 15 aces en route to setting up a last 16 encounter with Tunisia's Malek Jaziri.
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Second seed Kei Nishikori's title bid at the Wimbledon warm-up tournament ended in the second round after he pulled out with a rib injury before his second round match against Germany's Florian Mayer.
"I'm very sad to not be able to go on playing," Japan's Nishikori, who needed treatment during his first-round win against Lucas Pouille, told the Halle tournament's official website.
Nishikori said he was confident the injury would improve before the start of Wimbledon on June 27.
(Reporting by Pritha Sarkar, editing by Ken Ferris)