Defending champion Leonardo Mayer progressed to the second round of the German Open with a straight-sets victory over Spaniard Albert Ramos-Vinolas.
The unseeded Argentinian, who also won the tournament in 2014, secured a 6-3 6-2 success to set up a last-16 meeting with either Italian sixth seed Marco Cecchinato or Frenchman Gael Monfils.
Mayer's countryman Diego Schwartzman, the second seed, is also through to the next round, although he needed three sets to see off 19-year-old wildcard Casper Ruud.
The world No.12 won 6-4 2-6 6-2 and will play Daniel Masur next after he defeated fellow German Maximilian Marterer 6-3 6-4.
David Ferrer, finalist in 2014, was knocked out, losing 7-5 5-7 6-3 to 17-year-old German wildcard Rudolf Molleker.
Molleker's reward for defeating the experienced Spaniard is a second-round meeting with Jozef Kovalik after he dumped out fourth seed Damir Dzumhur 6-2 6-4.
Last year's runner-up Florian Mayer also exited the tournament on Monday, failing to capitalise on a strong start before losing 2-6 6-1 7-6 (7-4) to third seed Pablo Carreno-Busta.
