Maxime Cressy stunned world No 9 and top seed Holger Rune in three tough sets to reach the Montpellier ATP final on Saturday.
The French-born serve-and-volleyer came out on top 7-5, 6-7 (3/7), 7-6 (7/4) to reach his fourth tour-level final.
Cressy fired 15 aces in his two-hour, 36-minute win and should break the top 40 in the rankings next week.
The 25-year-old will be aiming to win his second tour-level title when he takes on Jannik Sinner in Sunday's final.
"Jannik Sinner is an incredible player like Holger Rune and everyone else in the tournament," said Cressy.
Earlier on Saturday, Italian world number 17 Sinner beat French 18-year-old Arthur Fils 7-5, 6-2 in his semifinal.
"He is very strong and has great groundstrokes," said Sinner who will be playing in his eighth final.
"Maybe I had a bit of experience on him in the first set and I got a bit lucky."