Latvia's Ernests Gulbis survived a few anxious moments in the final set but held his nerve to upset top-seed Mardy Fish 5-7, 6-4, 6-4 and win the Los Angeles International on Sunday.
Serving for the match at 5-2, Gulbis was broken by American Fish and then trailed 30-40 on serve at 5-4 before sealing victory.
"It means a lot to me. It's my second title," Gulbis said. "It gives me a huge boost in confidence."
Gulbis, who had knocked out second seed Juan Martin del Potro of Argentina in the quarter-finals, pumped his right fist in celebration after becoming the first unseeded champion in Los Angeles since Radek Stepanek in 2007.
The triumph was Gulbis's first victory over a top 10 opponent this season. Fish fell to 6-13 in ATP World Tour Finals.
"I've played a lot of matches the past month and half, so he came in a little bit fresher than me. I think that played a part," Fish said.
"But credit to him. He played well when he needed to. He got those two breaks early [in the third set], clearly which was big. I almost got him in the end... it wasn't meant to be."
Federer roars through in Monte Carlo clay debut
Seppi beats Tipsarevic in bizarre final
Nadal reaches Queen's last eight after rare blip
Djokovic battles through to round 4
Indian teenager on tour goes missing in LA