Luis Horna overturned the form book to beat home favourite Nicolas Massu for the first time and win the Movistar Open final in Vina del Mar, Chile.
Massu, who had not dropped a set in five previous ties against Horna, broke in the seventh game for an early lead.
However, Peruvian Horna fought back from 5-3 down, winning six straight games on his way to a 7-5 6-3 victory.
The win came in one hour, 52 minutes, and was Massu's second straight defeat in the final at Las Salinas club.
"Tomorrow is another day and I will forget about this and focus on my next goal which is the Davis Cup"
It was only Horna's second ever ATP title, having won at Acapulco last March, and was based on the impressive foundation of an 84% first-serve percentage.
"He has a lot of pressure whenever he plays here," said Horna.
"It is his city, he wants to win this tournament so badly. I had no pressure at all and only wanted to play my best tennis."
The defeat took Massu's record in finals to 6-9 as he prepares to defend his title in Costa do Sauipe, Brazil later this month.
"Today I was tense, slow, I was playing too short and you can't win like this," said Massu. "I still had an opportunity at 5-4 in the first but nothing happened.
"I know tomorrow is another day and I will forget about this and focus on my next goal which is the Davis Cup."