The 20-year-old grew in confidence through the three-hour contest after losing the first set and saved a match point before clinching his first victory over Humbert after defeats in their previous four meetings, including twice this year.
"After 5-5 in the first set, I was feeling I was going to be dead on the court. He was playing unbelievable shots ... I could have lost today," Fils said in his post-match interview.
Fils broke early to go 3-2 up in the first set but struggled on serve, handing Humbert a break in the next game with back-to-back double faults. But Fils then put pressure on world number 19 Humbert, who had to save four break points to hold twice.
It was Humbert who found the break though as he took the first set, with Fils struggling due to his injury.
The world No. 24 received some treatment in the second set as Humbert looked to break and take a 5-4 lead, going 40-0 up. But Fils dug deep to save all three break points, landing measured shots near the lines as the set went to a tiebreak.
Humbert went 6-5 up in the breaker and was serving for the match but Fils, now moving more easily, saved a match point with a spectacular backhand passing shot and won the next two points to take the set.
Fils pushed hard in the third set and Humbert saved two break points before his fellow countryman finally prevailed, taking a 5-3 lead before sealing the title with an ace.
"I am super happy, super proud of you," Humbert told Fils.
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