INDIANAPOLIS --It almost seemed right. Just as he had done so many times before, quarterback Peyton Manning had the opportunity to engineer a game-winning drive at Lucas Oil Stadium.

Only this time, it would be for the opposing team. But on the first play of the pivotal fourth-quarter series, his team down just six points, Manning threw an interception after his arm was hit when he released the ball.

That allowed Indianapolis to pull out to a nine-point lead, and by the time Denver pulled back to within one possession, it was too late, as an onside kick attempt failed with 12 seconds remaining in the game. Colts quarterback Andrew Luck took a knee to seal a 39-33 victory, dropping the Broncos to 6-1 on the season.

"We still had a chance there at the end," Manning said. "We did fight and hung in there. We can learn from it. We certainly have to improve from this game because we weren't as sharp execution-wise as we'd like."

The Broncos had their chances.

Even after Manning's interception allowed the Colts to make it 39-30, the Broncos offense responded quickly, driving all the way down to the Indianapolis 2-yard line. But a Ronnie Hillman fumble -- the third turnover of the evening for the team -- gave the ball back to Indy and allowed the Colts to run 1:35 off the clock and force Denver to use all three of its timeouts.

A 47-yard Matt Prater field goal moved the Broncos back within six, but the ensuing onside kick with just 12 seconds left on the clock failed.

"Anytime you turn the ball over (three) times, especially on the road, it's going to be tough," Head Coach John Fox said.

Earlier in the game, Manning fumbled when his arm was hit, but the ball was recovered out of bounds in the end zone -- which meant it was a safety, but didn't count against the turnover margin.

"That one was, among others, a couple of plays where we gave them some points and some field position," Manning said. "Ultimately that was just too tough to overcome."

The Broncos fell behind by as many as 19 points in the third quarter, but were able to claw back into the game thanks to key defensive stops down the stretch.

"I thought defensively we settled down," Fox said. "We started playing smarter, tougher football and executed better in the second half."

Key in the comeback was a forced fumble by safety Duke Ihenacho. He ripped the ball away from Colts running back Trent Richardson and recovered it himself, a takeaway the Broncos offense converted into a touchdown.

In the first half, the Colts scored 26 points. In the second, they were held to half that.

But the Broncos couldn't quite get all the way back on top, and mistakes were costly. What stood out to Manning is the fact that, even with the mistakes, the team "still somehow had a chance to win that game."

"I'd like to have seen it go to a two-point game down there toward the end and seen what would have happened," Manning said. "Never quite got to that point."

The Broncos got the Sunday Night Football scoring started when Manning found wide receiver Eric Decker -- who finished with a game-high 150 receiving yards -- for a 17-yard touchdown strike.

Denver fell behind 10-7, but a 12-yard score from Manning to tight end Julius Thomas put the club back ahead 14-10. Even after the safety, the Broncos still led, but a 20-yard touchdown from Luck to his fullback Stanley Havili in the second quarter gave Indianapolis a lead it wouldn't relinquish.

Six three-and-outs didn't help Denver's cause.

"I think they kind of kept us off balance a little bit and we weren't able to get into a rhythm for a while," Thomas said. "That's not us, that's not our identity and we have to clean that up."

Linebacker Von Miller -- who made his regular-season debut in the contest and finished with two tackles, a tackle for loss and two quarterback hurries -- said the toughest part is knowing the team didn't put its best foot forward.

"I think all phases of the ball, we could have done better," he said. "We could have had a better effort, but that's part of it. Get back in the lab, start working and get ready for Washington coming up."