The fifth-seeded Russian will face fourth-seeded Paul-Henri Mathieu, who beat Adrian Mannarino 7-6 (8), 7-6 (1) in an all-French semifinal.
"I think I'm serving well and I'm trying not to make silly errors,'' Tursunov said. "It's quite an improvement on the past.''
He had four aces in the first set and won 89 percent of his first-serve points.
Stepanek, seeded seventh, had four break points in the second set but failed to convert.
Tursunov will be playing his third final this season, while Mathieu will be in his first. Tursunov beat Mathieu in three sets in their only previous meeting.
Tursunov advances to Open de Moselle semifinals
Advocaat: We Can Beat Juve & Madrid
