NORMAN, Okla. -- Maybe Mother Nature was trying to impose a mercy rule. The weather was the only thing that could slow down No. 4 Oklahoma against Chattanooga.

Sam Bradford threw for 183 yards and two touchdowns, Chris Brown ran for three scores and only an hourlong rainstorm could slow down the Sooners in a 57-2 victory against Chattanooga on Saturday night.

The Sooners converted their first seven possessions into touchdowns and led 50-0 before a thunderstorm caused a lightning delay that extended halftime by 1 hour and 12 minutes.

Instead of stopping the game, both teams went through a glorified scrimmage in the second half -- except one team was trying not to score.

"That's always a difficult situation in the second half when you're up 50-0 at halftime. You want your [backups] to move it but you don't want to be a bad guy and be throwing it all over the place and taking advantage of what's there," Oklahoma coach Bob Stoops said. "You know, you do the best that you can."

Oklahoma seemed to be pulling back on the reins after reaching former coach Barry Switzer's proverbial "half a hundred," putting fullback Matt Clapp at tailback for the next series. Dominique Franks also called for a fair catch on what seemed to be a returnable punt.

But after halftime, Oklahoma's starters were back on the field -- even if their production level fell off sharply. They managed only two first downs on their first three drives before backups started filtering in.

Stoops said he decided the starters still needed to be sharp next week, no matter what the score was at the time.

"Those are all tough decisions. That's just the way it goes," Stoops said.

Bradford completed 17 of 22 passes, including a 3-yard score to Quentin Chaney and a 7-yard TD to Manuel Johnson on fade patterns. DeMarco Murray had a pair of 1-yard scoring runs, one of them following a 49-yard scamper, and finished with 124 yards on 15 carries.

Brown also had touchdown runs of 10 and 9 yards.

"It's the first time out this year, trying to kind of avenge a loss at the Fiesta Bowl last year, so there was a lot of preparation put in to come out and play well," said Bradford, referring to a 48-28 loss to West Virginia this January.

The Mocs scored their only points after Oklahoma's first drive of the second half, when punter Mike Knall tracked down a bad snap in the end zone and knocked it out of bounds for a safety.

Chattanooga coach Rodney Allison talked earlier this week about hoping to make it a game into the second half, like the Mocs did last year at Arkansas, and trying to avoid injuries. Neither one worked.

Tailback Erroll Wynn, who took the place of injured starter Bryan Fitzgerald, broke his wrist in the second quarter and starting quarterback Jare Gault came out with a stinger in the third quarter. Allison hopes both will be able to play next week.

Oklahoma athletic director Joe Castiglione said there was never any talk of calling off the game at halftime, and both coaches favored going on with it.

"We have got a bunch of fighters ... ," Allison said. "A nice trait of ours is that our players have always played until the end of the game. They came back and played hard the whole game. From that standpoint, I was pleased."

All fans were asked to leave the seating area of Owen Field during halftime, although they were told that re-entering would not be allowed if they left the stadium.

A dozen or so remained in the student section, and others huddled under overhangs, in tunnels and on the concourse.

The rest left. They had seen enough already anyway.

Chattanooga, Oklahoma's first Championship Subdivision opponent since Stoops' debut in 1999, had only one first down, one completed pass and negative yardage on its first seven possessions.

The Mocs ended up with 36 yards, three completed passes and only one more first down.

"It was a great win for us but at the same time we can't beat our chests because it was just our first game," Franks said. "We've got a new opponent coming in the second week that we've got to get this game behind us."

After backup quarterback Joey Halzle's 36-yard touchdown pass to Iglesias made it a 50-point lead, Oklahoma's mascot ponies -- Boomer and Sooner -- weren't even sent onto the field with the Sooner Schooner for their usual celebration. Unlike all the first-half scores, no fireworks were set off after Brown's 1-yard TD run put Oklahoma up 57-2.

The Sooners ended up playing Chattanooga -- which after a 2-9 season was hardly a threat like fellow conference member Appalachian State, the three-time FCS champions -- after Middle Tennessee turned down an opportunity to be Oklahoma's season-opening foe.

After all, they'd been there before. They lost 59-0 in Norman two years ago.

"Everything isn't always perfect or how you want it to be," Stoops said. "You deal with it the best you can. ... I don't know that anyone's complained about our schedule over the years. We've played a fairly exciting schedule and have got some great games coming up.

"Every now and then you get caught in a situation that isn't the best. That's the way it goes."