Coco Gauff defeated fellow American Jessica Pegula in straight sets, 6-2 6-4, to capture her second Cincinnati Open women's singles title.
It means the world No 4 becomes just the third player in the Open Era, after Serena Williams and Victoria Azarenka, to win multiple titles in Cincinnati.
Pegula had beaten defending champion Iga Swiatek in the semi-finals, while Gauff disposed of unseeded Sara Bejlek - who had knocked out world No 1 Aryna Sabalenka - to set up the first all-American women's final in Cincinnati for 56 years.
Gauff stormed out to a 5-0 lead in the first set, taking it 6-2. Pegula battled back to 5-4 in the second before Gauff, who converted five out of six break points in the contest, closed out the win.
"I think it was a long journey, but I'm happy," Gauff said. "I think it's night and day, the player I was last year to now.
"I don't think that this is an indicator that I'm going to do well in New York [at the US Open]. Just knowing the quality wins that I had this week, hopefully I can use that experience."
Gauff had five wins in straight sets in Cincinnati.
"I thought she just played at a really high level and didn't really have many dips," Pegula said. "I didn't really think I played bad.
"The more you construct the point [against her], the worse it is because she almost likes to run. It was tough today. A dangerous, confident Coco is going to New York."
The head-to-head series between Gauff and Pegula is now tied at five apiece. Sunday was their second meeting in a final, with Gauff winning at Wuhan last year.