Kei Nishikori broke American John Isner once in the second set and again in the third set and that was enough for the rising Japanese player to claim the Citi Open title in Washington DC.
The second-seeded Nishikori beat the big-serving Isner 4-6 6-4 6-4 to celebrate his third title of the season and 10th of his career.
"It's been an amazing year so far," said the 25-year-old Nishikori, who will move up to fourth from fifth in the world rankings.
"I've had some good Grand Slams, too."
Nishikori now looks forward to taking the next step at the US Open, where he lost to Marin Cilic in the final last year.
"I defend the final in the US Open, so I will try to keep it going," he said about his ranking points.
"I'm playing well and I'm looking forward to keeping it going at the US Open."
The Japanese broke Isner in the first game of the second set, and again early in the final set and outsteadied him on the hardcourt to sweep to victory.
Isner, coming off a tournament win last week in Atlanta and playing his 10th match in 12 days, fired 18 aces to Nishikori's five, but the cool, calm Japanese was sharp with 23 winners and only 13 unforced errors in nearly two hours of tennis.
It was another D.C. disappointment for 30-year-old Isner, who lost in the Citi Open final for the third time in six years.