Qualifier Florian Mayer defeated sixth-seeded Viktor Troicki 6-4, 7-6 (4) in the opening round of the Mercedes Cup on Tuesday.

Troicki was the runner-up last season, when the tournament was still played on clay. It is now played on grass, as a tuneup for Wimbledon. Troicki went down despite serving 10 aces. He lost his footing several times and produced a double-fault that allowed Mayer to serve out the match.

Wild card Juan Martin del Potro fired 12 aces and cruised past Grigor Dimitrov 6-4, 6-2. Mikhail Youzhny beat fifth-seeded Feliciano Lopez 7-5, 6-3 and John Millman defeated eighth-seeded Lucas Pouille 6-7 (3), 6-3, 6-4.

Taylor Fritz beat Fabrice Martin 3-6, 7-6 (6), 6-1 and will next play top-seeded Roger Federer, who had a bye into the second round. Federer is coming back after a back injury that forced him to skip the French Open.

In the late match, Jan-Lennard Struff came from behind to beat Marcos Baghdatis 4-6, 6-1, 6-4.