TEMPE, Ariz. — There were few surprises in Chris Petersen’s first season as Washington’s football coach. The Huskies won the games they were supposed to win. They lost all five of their regular-season matchups to ranked Pac-12 Conference teams.

In the buildup to Friday night’s TicketCity Cactus Bowl, the Huskies appeared loose and confident, not surprising after two blowout victories in November to end conference play.

What happened then, in a 30-22 loss to the Oklahoma State Cowboys, was nothing short of stunning.

In Washington’s most confounding performance of the season, Oklahoma State built a 24-0 halftime lead as the Huskies looked like a team still hibernating after a five-week layoff. UW was sharper in the second half, but the early struggles were too much to overcome.

“We were just getting our teeth kicked in on offense from the very start,” Petersen said. “We couldn’t get anything done.”

The Huskies, who entered the bowl game as a 6½-point favorite, ended the season with an 8-6 overall record. Their defense missed many tackles in the first half. Their quarterback missed many open receivers.

“We were just too relaxed. Too relaxed,” sophomore quarterback Cyler Miles said. “We were kind of back on our heels, going with the flow, kind of like it was practice. It was all of us. I’m not singling nobody out; all of us were too relaxed in the first half and as you can see, we can’t do that.”

The Huskies deserve credit for making a game of it late. They were a new team in the second half.

On the opening drive of the third quarter, junior receiver Jaydon Mickens took a handoff on a reverse and scored on a 31-yard dash to get the Huskies on the board. That cut the Cowboys’ lead to 24-7.

UW sophomore John Ross III returned a kickoff 96 yards late in the third quarter to get the Huskies to 27-14.

The Cowboys (7-6) added a third Ben Grogan field goal, this from 34 yards, to extend their lead to 30-14 with 5:54 left in the game.

UW answered when Miles found Mickens on a bubble screen for a 16-yard touchdown with 3:29 left. The Huskies converted the two-point try when Miles hit Deontae Cooper, cutting OSU’s lead to 30-22 with 3:29 left.

On the Cowboys’ next possession, facing a third-and-two in their own territory, they threw to 300-pound defensive tackle James Castleman for a stunning 48-yard gain to the UW 17. That appeared to seal the win for the Cowboys, but a fourth field-goal try by Grogan, this from 27 yards, was off the mark.

That gave UW faint hope with 43 seconds left from its own 20-yard line.

Miles drove UW to its own 45-yard line in the final 20 seconds, but his final throw was intercepted by OSU’s Kevin Petersen, clinching the Cowboys’ win.

“We got going,” Miles said, “but unfortunately it only happened in the second half.”

Miles, wrapping up his first season as the Huskies’ starting quarterback, was as bad as he’s ever been in the first half. The Cowboys outgained UW 177-17 in total yards in the first quarter, and the Huskies didn’t pick up their first first down until six minutes into the second quarter.

UW’s rushing attack was mostly shut down, too. Dwayne Washington was held to 42 yards on 13 carries after three straight 100-yard games.

Miles was 8 of 13 for 76 yards in the first half. He was better in the second half, finishing 25 of 38 for 268 yards with one touchdown, an uneven performance in an inconsistent season that will do nothing to quiet the critics crying for a newer, younger quarterback to emerge in 2015.

Backup quarterback Jeff Lindquist came in for one Hail Mary throw on the final play of the first half, and Petersen hinted he at least gave passing consideration to making a change at quarterback. Ultimately, though, he wanted to give Miles a chance to get into a rhythm.

“The second half, we got some things going. It was better,” Petersen said. “But the first half, there was zilch.”

Defensively, the Huskies — second in the nation in sacks — couldn’t get consistent pressure on Oklahoma State’s freshman quarterback Mason Rudolph, making his third start. UW also whiffed on a number of open-field tackles.

Oklahoma State had scored on the game’s opening possession, using an efficient 11-play, 84-yard drive to take a 7-0 lead on a 1-yard run by Castleman. The Cowboys took a 24-0 lead on Rudolph’s 47-yard touchdown pass to Brandon Sheperd in the final minute of the first half.

“We came in at halftime and we were like, ‘No, this is not us,’” junior linebacker Shaq Thompson said. “It was just lack of focus. … It did shock me a little bit. I wish we had started off better.”

Adam Jude: 206-464-2364 or ajude@seattletimes.com. On Twitter @a_jude.

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