Japanese teenager Kei Nishikori stunned American top seed James Blake 3-6 6-1 6-4 to win the Delray Beach International in Florida on Sunday.
Nishikori was playing in his first ever ATP final
The 18-year-old qualifier, ranked 244, is the first Japanese man in nearly 16 years to win an ATP event.
Blake, ranked 12th in the world, took the first set and appeared to be on his way to an 11th career title.
But Nishikori raced to a 4-0 lead en route to the second set and broke early in the third to close out the win.
"This is the best tournament in my life," said Nishikori. "I am so happy right now. I played eight matches in nine days but I didn't feel tired."
He hit cold winners at times you wouldn't expect them
Shuzo Matsuoka, who coached Nishikori when he was younger, was the last Japanese to win a tour event when he beat Todd Woodbridge in Seoul in April 1992.
Nishikori, who has been based in Florida since he began training at the Bollitierri Academy at the age of 14, was playing in his first ever ATP final.
"For an 18-year-old, the poise he showed is what impressed me the most," said Glenn Weiner, who coaches Nishikori.
"Against someone like James, and even against Sam (Querrey, semi-finals), he lost the first set, then comes right out at the beginning of the second up a break. It didn't faze him."
Blake said: "He played really well and didn't show any kind of nerves. I didn't feel like I returned as well as I had in past matches.
"One break in a three-set match says a lot on my part. I felt he'd be carefree and play like he had nothing to lose.
"After you save four match points in the semis you are playing with house money. He hit cold winners at times you wouldn't expect them."