Jim Litke AP columnist

INDIANAPOLIS - A large red welt glowered angrily above Peyton Manning’s left eyebrow.

As souvenirs go, this was one he could do without.

But as a painful reminder of just how tough it is to go through an NFL season unbeaten, well, it was just about perfect.

The abrasion was a parting gift from the San Diego Chargers, who not only stole the Colts’ perfect season Sunday, but reminded them how slippery the footing can be at the top of the pro football globe. The Colts played a few bad games against good teams and got away with it. They understand now that won’t work every Sunday.

“It’s something we need to respond to,” Manning said quietly in the aftermath of a 26-17 loss at home. “It leaves a really bad taste in your mouth. We’ve got to get it out.”

If the Colts still plan on wearing the Super Bowl crown they’ve been modeling most of this season, Monday can’t come soon enough. They were inept on offense early in the game, uncharacteristically sloppy in the late going and listless for long stretches in between. The only consolation, if there’s any to be had, is that this was as close to a total team failure as failures get.

Coach Tony Dungy took the blame for the decision to pass on a field goal and go for a score on fourth-and-1 with 8:38 left in the first half. When Manning wound up losing six yards on a bootleg, that cost Indianapolis an almost-certain three points, plus the three points the Chargers tacked on with a Nate Keading field goal seconds before halftime.

“That wasn’t very smart on my part,” Dungy said. “If we’d got those, it’s a different game.”

UNDEFEATED NO MORE      Chargers hand Colts first loss Kravitz: Colts can still be Super JT's Rant: Colts look vulnerable Litke: Peyton desperate to ditch losing feeling '72 Dolphins claim mixed feelings Defense drives San Diego's stunner Interactive: Compare Peyton with Eli

That was hardly the only what-if juncture where the Colts ran a stop sign. Manning’s biggest gaffe was getting called for intentional grounding with 3:16 left to play, when the Colts trailed 19-17, but had driven to the San Diego 23-yard line and within striking distance of a go-ahead score.

“The No. 1 thing there,” Manning explained, “is to try and not take a sack.”

So naturally, the Chargers sacked Manning on the next play, the last of San Diego’s four on the day. That 3-yard loss, added to the 12 yards assessed on the previous play for grounding, made a field-goal try academic.

Slide show   The Week in Sports Pictures The Giants on top of the football world, getting ready for the London Olympics and more. more photos

Just to make sure everybody felt bad, though, the defense let San Diego’s Michael Turner get around the corner on the second play of San Diego’s next drive. As he headed up the sideline, Turner outraced two defenders who had angles on him and shed a last-gasp tackle by Jason David like he was Gale Sayers.

“When you have guys out of place or you miss a tackle here, you’re going to get some long runs,” said safety Bob Sanders, whose punishing hits helped transform Indianapolis’ defense from pushovers to punishers. “It’s frustrating any time you give one up. Big plays kind of take the wind out of you.”

Manning wasn’t even born the only time a team went through an NFL season unbeaten. That was 1972, when the Miami Dolphins melded talent, desire and plenty of luck to run the table. They’re often thought of as one-season wonders, but the opposite is true. That Dolphins team played in three straight Super Bowls and won two of them.