After dropping serve three times as he lost the first set, the 27-year-old from Monaco gradually gained control of the match to claim his second title on the main tour, following his surprise victory at the Shanghai Masters in 2025.
For Lehecka, 24, the loss extended his poor record in finals to seven defeats from nine appearances. He has lost each of the past five.
The Czech had completely dominated Vacherot in a two-set victory in their last meeting in early October, in the semi-finals in Tokyo.
The first set on Sunday suggested that result might be repeated. Lehecka conceded only one point on his first three service games and proved superior in every aspect of the game.
Lehecka put pressure on Vacherot's serve throughout the match but the Monegasque saved all five break points he faced over the next two sets.
In both a single break was enough for Vacherot, who closed out the match on his first championship point.
"I ended up playing a really solid second and third set," Vacherot said. "I had to hold tight in the second set because even until the last game he had break points. Then I started serving much better in the third set and that helped me a lot."
"I hit really good shots at the right moments," he said. "Sometimes it's about not playing perfect for the whole match and just playing good when it matters."
The victory over Lehecka, who entered the tournament ranked No. 21 in the world, was Vacherot's third against a top-25 opponent in Basel, where he also saw off 11th-ranked Rafael Jodar after a three-hour battle and world number 13 Taylor Fritz in the semi-finals.
