FORT WORTH, Texas (AP) — Trevor Knight and No. 4 Oklahoma were walking off the field at No. 25 TCU with their first loss of the season a few minutes after No. 3 Alabama lost.

No. 2 Oregon and No. 6 Texas A&M had already opened October with losses.

Because of all the upsets, the Sooners' 37-33 loss Saturday may not have been a fatal blow to their standing for the new four-team College Football Playoff. But it was certainly a jolt and a huge missed opportunity for Oklahoma (4-1, 1-1 Big 12).

"This isn't the defining moment of our season. There's a lot of football left," said Knight, the sophomore quarterback who lost for the first time in his 10 starts. "Who knows what's down the road. It's early in the season, a one-loss team can still make it."

Knight threw for 309 yards, but one of his two interceptions in the fourth quarter was returned 41 yards by Paul Dawson for the go-ahead score for the Horned Frogs (4-0, 1-0). Samaje Perine, who had three TD runs, was stuffed for no gain on a fourth-and-1 try from the TCU 22 with just over 3 minutes left in the game.

"I have no qualms about how our team played. We came in here ready to play," coach Bob Stoops said. "We knew it was going to be a big challenge. The bottom line is they made plays and we didn't."

Dawson's pick came with 14:12 left. The former high receiver reached up with both hands to grab the ball and raced untouched to make it 37-31. The Sooners got two points when Jordan Phillips blocked the extra point and Zack Sanchez returned it to the end zone.

"The guy made a heck of a play," Knight said. "There's not much you can do about that."

Dealing with cramps part of the game, Knight finished 14-of-35 passing. He ran 13 times for 61 yards.

Oklahoma will be back in North Texas next Saturday, taking on Texas in the Red River Rivalry game at the State Fair of Texas.

"I know for sure that if you keep losing, you're not going to have much chance of anything," Stoops said. "We take it week by week. We came in here knowing that we had to play our best to win this game. Period. We weren't looking at the end of the season."

The Sooners two years ago clinched a share of their eighth Big 12 title with a regular-season ending 24-17 win at TCU. They beat the Frogs at home 20-17 last season.

For Gary Patterson and the Frogs, they finally have a big attention-grabbing victory in the Big 12 Conference.

"It basically gives us confidence," dual-threat quarterback Trevone Boykin said. "Knowing that we can play with guys like OU, because a lot of Big 12 championships have went through there."

The former BCS-busting Frogs have won its first four games for fifth time in the last seven years under Patterson, but didn't have a win of this magnitude it its first two Big 12 seasons, when they were 6-12 in league games.

"They just straight outplayed us," Oklahoma defensive tackle Chuka Ndule said.

Boykin, who passed for 318 yards and ran for 77 more, fumbled on a keeper in the fourth quarter. But two plays later Chris Hackett had an interception for TCU before B.J. Catalon gave it right back on a fumble at the Frogs 46 with 6 minutes left.

The Sooners picked up a first down, on Perine's 6-yard run on third-and-1. But the freshman back who had 242 yards at West Virginia in the Sooners' last game two weeks ago, was stopped short when the Sooners needed only a yard.

Knight threw a 75-yard TD pass to wide-open Sterling Shepard in the first quarter that tied it at 14 after TCU jumped ahead 14-0 on its first two drives. Shepard had seven receptions for 215 yards, including a 53-yard catch to set up Perine's first TD run.

"They caught us with a couple of big plays early," Patterson said. "We had to change up some coverages and we finally got a chance to slow them down a little bit."