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Qualifier Buse won 7-6 (8-6) 4-6 6-3 in a little more than three hours against the No.6 seed in the ATP 500 tournament showpiece.

After Paul saved two break points in the opening game, the pair exchanged two breaks each as they were made to go through a tie-break in the first set.

The tie-break went in favour of Buse, who clinched the first with his third set point, but Paul's quality came to the fore in the second as he raced into a 4-0 lead.

The American did drop one service game, but he held his nerve to take the match to a decider, where Buse regained his rhythm.

He broke at the fifth time of asking in the second game, before converting another break point in the sixth, setting him well on his way to victory, which he sealed with his first championship point.

Elsewhere in Geneva, there was a better outcome for Paul's fellow American Learner Tien, who defeated Mariano Navone in the final.

No.4 seed Tien came from behind to win 3-6 6-3 7-5, after defeating Alexander Bublik and Stefanos Tsitsipas en route to the showpiece.