PULLMAN — Just when it appeared Washington State was poised to take another step toward bowl eligibility, the Cougars cast a spell of almost comical ineptitude upon themselves Saturday night.

When they were done with the self-immolation, they had been blown away, 52-24, by Oregon State, which won its fifth consecutive game.

The stretch clearly left Mike Leach, the second-year Cougars head coach, furious.

“Offensively, for two-thirds of the game, we played pretty well,” said Leach. “For one third of the game, we played about as bad as it’s possible to play.”

As for quarterback Connor Halliday, who struggled mightily during the fatal spell, Leach said, “I thought he gave in. We had adversity. It certainly wasn’t just Connor. We faced adversity and waved the white flag.”

Leach said the coaching staff has “to get it out of them and get it changed. You’ve gotta play a game 60 minutes.”

WSU fell to 4-3, and now faces No. 2 Oregon in Eugene this weekend.

This was a score that reminded a Dads Weekend sellout crowd that work remains to be done in the Leach rebuild. Particularly, mental toughness seemed to desert the Cougars too easily in this one.

“We need to learn as a team not to look at the scoreboard and play through adversity,” said WSU center Elliott Bosch.

“It’s really disappointing. We were playing 2½ good quarters. To kind of explode, it’s disappointing, it’s frustrating.”

Not that there weren’t physical errors aplenty. The Cougars committed six turnovers and another key play on a punt that went awry was as good as a seventh.

This game was anything but a blowout deep into the third quarter, a give-and-take, back-and-forth momentum-swinging affair that suddenly turned in floodgate fashion for the Beavers, who put up four touchdowns in the dizzying span of 5 minutes, 23 seconds to win going away.

When the Cougars weren’t turning the ball over, they found themselves completely unable to stop two Beaver staples — the fly sweep and the screen pass.

The Cougars had scored a pair of third-quarter touchdowns and their defense stopped OSU nicely, and WSU had a seven-point lead. But on third-and-10, the Cougars allowed the first in a passel of pivotal plays, this one a 31-yard pass from Sean Mannion to Caleb Smith to the WSU 41.

A third-down pass for a score, from Mannion to Kevin Cummings, tied it at 24 with 1:03 left in the third quarter.

It would turn disastrous in short order for the Cougars. They went three-and-out on their next series, and, at the WSU 34, deep snapper Alex Den Bleyker snapped the ball off-center, hitting a surprised blocking back Jared Byers in the chest. That fumble set up the Beavers at the WSU 27, and a couple of plays later, it was Brandin Cooks running it over from 8 yards out to make it 31-24, and OSU would never come close to surrendering the lead again.

Leach wasn’t definitive on what went wrong on the play, saying, “It was bad on our part. It’s basically my fault. We had two things going there. I allowed it to happen and shouldn’t have allowed it to happen.”

Pressed by a reporter on what the two things were, Leach said, “None of your business.”

Halliday then was intercepted on each of the next three possessions. It was three interceptions in five snaps, and 13 picks for the season against 14 touchdown passes as he battles a left-side injury incurred two weeks ago against Stanford.

Bud Withers: 206-464-8281 or bwithers@seattletimes.com