World no. 166 Matthias Bachinger defeated Kei Nishikori in the semifinals of the Moselle Open to set up a meeting with home favourite Gilles Simon.
Bachinger battled from a set down to win 2-6, 6-4, 7-5, breaking Nishikori in the final game of the match to seal the victory.
The German, 31, usually competes on the Challenger circuit but has reached an ATP Tour Final for the first time in his career.
Nishikori, who was defeated by Novak Djokovic in the semifinal of the US Open earlier this month, failed to convert any of his six break points in the deciding set. Bachinger was much more ruthless and converted his only break point of the third set to win the match.
Earlier in the day, France's Gilles Simon eased past Radu Albot 6-3, 6-1.
Simon, who defeated Richard Gasquet in Friday's quarterfinal, is a two-time winner in Metz after victories in 2010 and 2013.
The world No. 39 broke his opponent three times in the final set as he cruised to victory in one hour and 20 minutes.
He will look for his 14th ATP Tour title against Bachinger in Sunday's final.