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CINCINNATI -- The last thing that the St. Louis Rams wanted to see was Kyle Boller's helmet tumbling across the field.

Boller played better Thursday night in his second game filling in for Marc Bulger, completing a flurry of short passes during a 24-21 victory over the Cincinnati Bengals. He also had one moment of bravado that made the Rams shudder.

He refused to duck.

Boller got his helmet knocked off on a hit by linebacker Keith Rivers at the end of an 8-yard scramble, waiting too long to start his slide. Unfazed, Boller got to his feet, found his helmet and completed his next two passes, including a 3-yard shovel pass to running back Samkon Gado for a touchdown.

"I could have slid a little earlier," said Boller, who was 14 of 20 for 96 yards. "It is what it is. My chin strap hit just above my eyes. It was a good scramble, but maybe if I can get down a little sooner, the coaches would like that."

No kidding.

"I was just trying to get to the ball," said Rivers, who had his jaw broken on a hit from Pittsburgh's Hines Ward last season. "It wasn't anything intentional."

The Rams lost Bulger to a broken pinkie finger on his passing hand before the last game and couldn't afford another quarterback setback. Bulger is hoping to be ready for the season opener Sept. 13 at Seattle. Boller struggled as his replacement last week in a 20-13 loss to the Falcons, but seemed much more comfortable against the Bengals.

"He moved the team," coach Steve Spagnuolo said. "He drove us down there after the bad start. When you score on a drive, the quarterback deserves the credit."

Both teams were missing their starting quarterbacks, turning the game into a preview of how it might be if their injuries linger. The Bengals were reminded that they really need Carson Palmer back for their opener against Denver.

J.T. O'Sullivan was sacked three times, lost a fumble and had two passes batted away at the line. His best moment was an improvised underhand pass to running back Brian Leonard that went for 25 yards and set up a touchdown. O'Sullivan was 7 of 13 for 94 yards while playing into the third quarter.

With Palmer sidelined the last two games by a sprained left ankle, the offense has moved the ball in spurts but failed to get many points because of penalties and mistakes. O'Sullivan's fumble at the Cincinnati 20-yard line set up the Rams' second touchdown.

"We've just got to find a way to eliminate it," O'Sullivan said. "It puts you in such a disadvantage any time you turn the ball over. That's one of the things that has to change immediately."

Running back Bernard Scott, a sixth-round draft pick from Abilene Christian, had a fumble that safety James Butler returned 73 yards for a touchdown. Butler also intercepted one of Jordan Palmer's passes in the third quarter and returned it 68 yards before the third-string quarterback tackled him.

The Bengals have lost five fumbles and thrown three interceptions in three preseason games.

"When you turn the football over, you have a difficult time winning, whether you're playing in the regular season, the preseason, junior high, sixth grade, whatever it is," coach Marvin Lewis said.

Quan Cosby, an undrafted receiver from Texas, returned the Rams' first punt 49 yards for a touchdown, breaking through the front line of defenders into the clear. He ran past punter Donnie Jones to get to the end zone.

Jones also had a punt returned 44 yards by Tom Nelson in the third quarter.

Game notes

Rams K Josh Brown was wide left on a 50-yard field goal try at the end of the first half and wide again on a 51-yard attempt with 3:10 left in the game. ... Bengals S Chinedum Ndukwe suffered a shoulder injury in the third quarter. ... Chris Henry caught a 54-yard touchdown pass from Jordan Palmer in the fourth quarter, beating rookie CB Bradley Fletcher down the left sideline. Henry has all three of the Bengals' touchdown catches in the preseason.