PULLMAN, Wash. — On a snowy afternoon in the Palouse, Stanford’s chances of reaching the Pac-12 title game took a major hit.

After No. 25 Washington State outlasted the No. 18 Cardinal 24-21 Saturday, head coach David Shaw blamed himself for being too conservative with his play-calling.

He wanted to stick with the ground game, but his team was repeatedly one block from breaking some big runs, he said. “We should have mixed it up a little bit (with passes). It’s completely my fault. I didn’t give our guys a chance to be successful today.”

Stanford tailback Bryce Love returned after missing a game with an ankle injury, but, except for a 52-yard touchdown run, he was almost completely shackled. It didn’t help his Heisman Trophy chances that, on his other 15 runs, he netted just 17 yards.

He said he felt fine even though he was seen hobbling on the sideline. “Washington State’s defense played really well, and it was a great battle,” he said after emerging from a long postgame treatment. “A few plays here or there could have made the difference, and we didn’t make the plays we needed to.”

Stanford (6-3, 5-2 Pac-12) isn’t quite dead yet in the Pac-12 North race. It has to beat Washington next Friday and hope the Huskies beat Washington State in the Apple Cup.

The Cougars (8-2, 5-2) needed a big game from quarterback Luke Falk, and they got it. He completed 34 of 48 passes for 337 yards and three touchdowns.

“There’s a reason he’s the Pac-12 career passing yard record holder,” Cardinal linebacker Bobby Okereke said.

K.J. Costello made his second start at quarterback for Stanford but completed just 9 of 20 passes for 105 yards with an interception. He scored a touchdown on a 14-yard run after his own fumble bounced back into his hands.

“As a team we were riding on waves of momentum,” the redshirt freshman said. He said his team had multiple chances “to put the game away, to make plays, to really take charge. We didn’t do it.”

The defeat snapped Stanford’s five-game winning streak, and the Cougars won it with an impressive 94-yard drive. Trailing 21-17 following Okereke’s 52-yard interception return for a touchdown, WSU got a key 17-yard pass from Falk to Tay Martin on 3rd-and-14 at its own 14.

With just under seven minutes left, freshman receiver Jamire Calvin took an 11-yard pass from Falk and performed a front-flip into the end zone.

Stanford had the ball for just 11 scrimmage plays in the fourth quarter, the last being a desperate pass by Costello that was picked off by Frankie Luvu with 35 seconds left.

Moments into the second quarter, Love shot through the right side for his long touchdown and a 7-0 lead. It was the 10th straight game, dating to last year, that he had a run of at least 50 yards.

Stanford converted on third down just 3 of 12 times. On its first four third-down opportunities, Stanford had an illegal substitution penalty followed by an unsuccessful run; a pass that was nearly picked off; a delay-of-game penalty, followed by an unsuccessful run, and a false-start penalty, again followed by an unsuccessful run.

The Cardinal failed on their only two third-down opportunities in the fourth quarter, the latter when Shaw called a run on 3rd-and-5 near midfield. Love lost two yards.

“In hindsight we should have had more opportunities — throwing the ball,” Shaw said.

Okereke’s pick-six put Stanford in the driver’s seat late in the third quarter. The Cougars gambled, as they often do, on a 4th-and-1 play at their 48, but he jumped the route run by Tavares Martin Jr. and grabbed Falk’s pass. It was his first career pick.

“We can still win the North,” Okereke said. “Got to get back to the drawing board this week.”

Tom FitzGerald is a San Francisco Chronicle staff writer. Email: tfitzgerald@sfchronicle.com Twitter: @tomgfitzgerald

Stanford schedule