PULLMAN, Wash. (AP) Mike Leach and his team were engulfed in a sea of crimson on the turf of Martin Stadium, reveling in a rare occurrence for Washington State football.

An upset victory 25 years in the making was worth celebrating in grand fashion. And, it proved that these Cougars are true contenders for a Pac-12 title.

''It's exciting. I'll enjoy it tonight. I'll probably enjoy it a little in the offseason,'' Leach said.

Luke Falk threw for 340 yards and two touchdowns, Erik Powell kicked a 32-yard field goal with 1:40 left and No. 16 Washington State beat No. 5 Southern California 30-27 on a wild Friday night.

With the national stage to themselves, the Cougars showed they were legitimate, stopping USC star quarterback Sam Darnold and pulling off their first regular-season win over a top-five opponent in a quarter-century. The last time a top five team was handed a loss by Washington State was 1992 when the Drew Bledsoe-led Cougars rolled rival Washington in a driving snowstorm.

Washington State (5-0, 2-0) had lost 15 consecutive home games against ranked opponents. This was its first win over the Trojans since 2002 - that game also finished in a 30-27 Cougars victory.

''We just showed that we were the better team tonight,'' Washington State defensive lineman Hercules Mata'afa said.

Falk was excellent against the pressure from Southern California (4-1, 2-1) most of the time, but it was a key 35-yard run from Jamal Morrow that set up Powell's winning field goal.

Falk finished 34-of-51 passing, while Morrow added 91 yards rushing on six carries. The duo combined to give the Cougars the lead early in the fourth quarter, with Falk finding Morrow for a 23-yard TD on a shovel pass and run. The drive included a key third-and-6 conversion early in the possession and a fourth-and-3 on Falk's pass to Kyle Sweet for 12 yards.

''I think it's just a stepping stone. We expect to win games like this,'' Falk said. ''Hopefully from here on out going forward guys will continue the tradition of competing in games like these. Right now it's a stepping stone.''

Darnold struggled through a miserable night. Darnold was 15-of-29 passing for 164 yards and an interception. He has thrown eight interceptions in five games after throwing nine interceptions all of last season.

Darnold ran for a pair of touchdowns, including a 2-yarder with 5:01 remaining that tied it at 27. But he couldn't pull off a final rally, fumbling when he was sacked deep in Washington State territory with 1:27 left. Falk took two kneel downs and the party erupted.

''We knew what they were going to run, it was just a matter of executing it,'' Darnold said. ''They made more plays than we did.''

Darnold had one drive in the fourth quarter that showed why he's coveted by the NFL. He stayed in a collapsing pocket on fourth-and-13 and Tyler Vaughns made a leaping catch across the middle in traffic for 15 yards to the Washington State 27. Darnold hit Vaughns for 26 yards on the next snap and two plays later Darnold ran for a score.

Playing without three of his starting offensive linemen, Darnold was flustered and at times appeared rattled by the pressure from Washington State's defensive line. He was sacked only twice but was forced to move in the pocket regularly, disrupting the timing of the pass game.

USC was already without starting left tackle Toa Lobendahn before starting right tackle Chuma Edoga limped off late in the first quarter after a wayward flea flicker that ended up being an intentional grounding penalty and a 14-yard loss.

It got worse for the Trojans when Viane Talamaivao was shaken up early in the second quarter and also did not return.

''Got a bunch of hurt kids right now in that locker room,'' USC coach Clay Helton said.

Southern California's Ronald Jones had 128 yards rushing and an 86-yard touchdown, but was mostly a non-factor outside of the long run.

THE TAKEAWAY

USC: The Trojans could not overcome injuries to a number of their starters. Along with being down three offensive linemen for most of the game, the Trojans played without starting outside linebacker Porter Gustin and starting wide receiver Steven Mitchell due to injuries. While USC has supreme talent, its depth is being tested.

Washington State: The Cougars benefited from a solid defensive performance. They entered the week 18th in the country in yards per play. Take away Jones' 86-yard run and the Cougars held the Trojans to under 250 yards total offense.

TURNING POINT

The biggest plays may have come from Washington State's defense. Late in the first half after Falk was intercepted at his own 3-yard line, the Cougars defense held USC out of the end zone and forced a short field goal to take a 17-10 lead. The Cougars were able to pull even at halftime on Morrow's 1-yard run with 13 seconds left in the half.

RECORD WATCH

Falk added to his list of Pac-12 records, passing Sean Mannion for the conference lead in pass completions. He also moved into a tie with Marcus Mariota for second in career touchdown passes with 105.

UP NEXT

USC: The Trojans return home for two straight games beginning with Oregon State next Saturday.

Washington State: The Cougars don't get much of a break, traveling to Oregon next Saturday.

Copyright 2017 by STATS. Any commercial use or distribution without the express written consent of STATS is strictly prohibited.