INDIANAPOLIS - The Indianapolis Colts' defense appeared vulnerable for the first time this season during a less-than-stellar opening quarter.

It dominated the rest of the way, knocking St. Louis quarterback Marc Bulger from the game and setting up Peyton Manning and the offense.

"We made some big plays," Colts coach Tony Dungy said. "We got the turnovers. We got the momentum."

The Colts rallied from a 17-point first-quarter deficit Monday night by forcing four turnovers, putting the offense in good field position throughout the second half and converting St. Louis' biggest mistakes into four touchdowns as they routed the Rams 45-28.

"Things changed when the quarterback went out," said cornerback Nick Harper, whose interception and fumble recovery each led to touchdowns.

"And when the backup came in, we didn't feel he came here to play," he said. "We wanted to show him that he needed to be on the bench."

While the Colts (6-0) remained the NFL's only unbeaten team and put themselves in position for the franchise's first 7-0 start, they certainly didn't follow the usual script.

Bulger led St. Louis (2-4) over, around and through the Colts' vastly improved defense in the first quarter. The result: A unit that allowed two touchdowns and 29 points in its first five games surrendered two touchdowns and 17 points in 15 minutes.

The Rams were so efficient, it didn't even look as though they missed coach Mike Martz, who was resting back home with a bacterial infection of his heart valve, or wide receiver Isaac Bruce, who was out with a toe injury.

But they clearly missed Bulger, who sprained his right shoulder on Cato June's interception return early in the second quarter. Bulger was steamrolled by linebacker David Thornton's block and was replaced by the mistake-prone Jamie Martin early in the second quarter. St. Louis was never the same.

"When you throw him into a situation like this - a hostile environment and a very big game for us against a very good defense - his reads may not be the same as our No. 1 guy," receiver Torry Holt said.

Martin did what he could, completing 17 of 21 passes for 134 yards with one touchdown - although two of his incompletions were interceptions.

That was the crack the Colts' offense needed to right itself.

Manning was 22-of-32 for 191 yards with two touchdowns, including a 6-yarder to Marvin Harrison that broke a tie with San Francisco's Steve Young and Jerry Rice for the NFL record for most TDs by a passer-receiver duo with their 86th. Edgerrin James ran 23 times for 143 yards and three touchdowns, and Dominic Rhodes scored on a 1-yard run.

But it was those pesky mistakes that cost the Rams.

"If you lose your starting quarterback, your chances aren't good," Rams running back Marshall Faulk said. "It's not even the interceptions as much as it was the injury. That was like a double-whammy right there."