The 21st seed, who won the Barcelona Open in April, added the Cincy crown to his growing list of achievements with a topsy-turvy 6-3 1-6 6-0 victory over Frances Tiafoe in Ohio.
Fils became the third Black man to win a Masters 1000 title, joining Ben Shelton, who won the Canadian Open twice, and Jo-Wilfried Tsonga, who won Paris in 2008 and Canada in 2014.
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"That feels good," said Fils, who dominated the deciding set to end France's 12-year wait for a Masters 1000 title. "There's a lot of training, a lot of sacrifice. Injury. To be able to win a title like this, it means a lot to me.
"I don't have any words to describe this. It feels so good. A little bit of relief as well."
Fils made a flying start by breaking early to establish a 3-0 lead in the opening set before Tiafoe got on the board with a hold of serve.
The Frenchman maintained relentless pressure from the baseline, attacking Tiafoe's second serve and forcing errors as he moved 5-3 ahead. Fils was untouchable on serve, closing out the set with three successive aces without dropping a point in the final game.
Tiafoe, playing in his second Cincinnati final, responded in kind in the second set.
The 28-year-old broke in the second game en route to a 3-0 lead, with his forehands pulling Fils wide. Although Fils got on the board with a hold to love, the 17th seed Tiafoe broke again for a 5-1 advantage before forcing a decider.
Fils quickly regained control in the third set, breaking twice to race into a 4-0 lead as Tiafoe's backhand errors piled up.
The 22-year-old's pace and movement proved too much for the American, and he closed out the match with a bagel final set after a lengthy rally to lift the trophy.
Tale of the Tape
Now 32-10 for the year, Fils is up eight spots to fifth in the ATP Live Race To Turin as a result of his run.
'Fils is like a ballet dancer'
Annabel Croft, speaking on Sky Sports Tennis:
"He talked about the sacrifices he made and the injuries he has had but what a performance that was in the final set. He played flawless tennis in the first set but he regrouped so well in that final set and breath-taking movement to watch him courtside.
"He's so agile, he's like a ballet dancer, and we saw every kind of shot that he could possibly come up with to win this title and to take on a home crowd as well it was really impressive."
Croft added: "He's so mature on the court. He's physically very mature and that was the aspect for me just how well this guy moves across the court. It's very dynamic. It's the take-off speed but it's also the agility. He can be on the front foot and attacking, but when he's pushed defensively he can turn on a sixpence and then put in the slices and defend so well."
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