Dominic Thiem earned what he called his career-best grass court win on Friday, defeating Russian Mikhail Youzhny 3-6 6-4 7-5 to earn the first semi-final of his career on the surface.
Thiem, the world No.7 thanks to a French Open semi-final last week, will await an opponent as Roger Federer faces German Florian Mayer.
Thiem won only his fourth career grass match, going through in just less than two hours.
“This was the biggest win of my career on grass,” Thiem said after beating the 2002 Stuttgart champion (on clay).
“There were a lot of ups and downs. I was close to losing in the second set with break points and at 5-5 in the third.
“I’m happy with my fighting spirit and happy with this whole win.”
The 22-year-old winner was stunned by his level on the unfamiliar surface: “Grass is different for me. I’m unbelievably happy with this semi-final. Anything that comes now is a big bonus.
“Both Federer and Mayer are very good on grass. Mayer is a bit unusual with his two-handed slice. He’s very uncomfortable to play.
“It’s not nice to play Roger on any surface. He is the best on grass. If I play him I have no expectations.”
Thiem beat an ailing Federer on Rome clay in May, but said that upset means little: “Clay is my surface, I feel very confident against almost all players.”