Aprilia's Eugene Laverty won race two in Laguna Seca to go second in the World Superbikes championship table.
The Northern Irishman overtook Davide Giugliano (Althea) and championship leader Tom Sykes (Kawasaki) in the last four laps seal an entertaining victory in California.
Yorkshireman Sykes, who won an incident-hit race one on Saturday, led for most of the race, but dropped down the field after being overtaken by Laverty and in the end finished fourth.
With two rounds to go, Sykes remained at the head of the championship standings, 23 points clear of Laverty, who moved second just a point ahead of team-mate Sylvain Guintoli.
Laverty told BBC Sport: "I wasn't sure I could do that as I didn't have great grip but it just shows the power of the Aprilia.
"That was one of the best races of my life and I had to work so hard over the last few laps."