Philipp Kohlschreiber beat Alexandr Dolgopolov 6-3, 6-3 in the only completed match in the first round of the Mercedes Cup.
The start of the other matches has been delayed due to heavy rain.
Top seed at the tournament Rafael Nadal will go straight into the second round.
Nadal offered these thoughts on the tournament.
"The first tournament I am going to play on grass is always a very tough one, a very difficult one, you need to adapt and you know it is something that I need time on court. I need to spend hours on court to feel myself comfortable on grass, the movements and the way that I hit the shots but the only way to make that happen is to spend time on court."
The Stuttgart tournament is being played on grass for the first time and is a build-up for the Wimbledon Championships.
