Andrew Furney's 41-yard field goal with 3:03 remaining vaulted Washington State past No. 25 Southern California, 10-7 on Saturday.
Damante Horton returned an interception 70 yards for a touchdown to provide Washington State with its lone touchdown.
Connor Halliday completed 26-of-38 passes for 215 yards and two interceptions and Kristoff Williams caught six passes for 56 yards for the Cougars (1-1, 1-0 Pac-12), who fell to Auburn, 31-24, last week.
"Both sides were dominating up front, and it was hard to scratch and eke something out," Cougars head coach Mike Leach said.
USC's quarterback controversy continued on Saturday with Cody Kessler under center in the first half and Max Wittek taking over in the second half.
Kessler was a dreadful 8-for-13 for 41 yards and an interception and Wittek finished 3-for-8 with a crucial interception on the Trojans' final possession.
"It takes time. We don't have (Matt) Barkley any more. New quarterbacks are coming in," USC wide receiver Marqise Lee, who tallied just 27 receiving yards, said.
Once again, the USC defense was stellar, limiting the Cougars offense to three points on just 222 total yards.
The Trojans (1-1, 0-1) will host Boston College on Sept. 14.
USC scored on its first possession of the second quarter. George Uko forced a Halliday fumble on the Washington State 36 and Devon Kennard returned it to the Cougars' 22-yard line.
After Tre Madden was tackled one-yard shy of a first down on 3rd-and-long, the shifty running back picked six yards on fourth to put the ball on the Washington State 7-yard line. Justin Davis was then stopped after picking up three yards before Kessler broke the plane from four yards out to give USC the lead.
Later in the first half, Horton picked off Kessler and returned it 70 yards to tie the game with 27 seconds left.
The Trojans marched 60 yards down the field on their opening possession of the second half, but came up empty as Andre Heidari had his 32-yard field goal attempt blocked.
USC had a chance to take the lead once again and Heidari lined up for a 43- yard field but pushed it left.
After the teams traded empty possessions, the Cougars finally took the lead.
Halliday found Dom Williams down the left side line for a 50-yard gain to put the ball on the USC 29, and after Kristoff Williams was stopped short of a first down, Andrew Furney drilled a 41-yarder to put WSU on top.
On the ensuing drive, a pass interference penalty gave USC a first down at its own 27. Madden then gained five yards with a rush up the middle, but Wittek was picked off on the next play, all but sealing the win for the Cougars.
This was the first meeting between the schools since 2010 ... Washington State is 13-57 all-time against USC ... USC was without injured running back Silas Redd, who is recovering from offseason knee surgery ... Madden rushed for 150 yards on 32 carries.