2019 finalist Andrey Rublev got off to a flyer in Hamburg on Monday with a comprehensive 6-3, 6-3 win over qualifier Tennys Sandgren.
But it was another disappointing day for South African Kevin Anderson, beaten 6-4, 0-6, 6-4 by American Tommy Paul.
Rublev controlled the game throughout with 26 winners and 18 unformed errors to bounce back after his loss in Rome last week.
Another qualifier, Pablo Cuevas, had san eventful match, beating Taylor Fritz 6-4, 6-2 in 80 minutes.
In matches today, young gun Felix Auger-Aliassime is up against Lorenzo Sonego.