The smile came back.
Two weeks after hearing a resounding chorus of boos from the home crowd and less than a week after watching his offensive coordinator, friend and mentor get fired, there's been a sudden and significant change in Indianapolis.
''The fun is in the winning and whenever you're able to move the ball and stay in rhythm, you're having fun,'' Allen said Monday. ''Andrew was having fun.''
Through the first eight games, the three-time Pro Bowler looked lost.
He was turning the ball over at an alarming rate, ended up on the injury report with two different ailments and had only won one of his first six starts and the usually unflappable quarterback blamed himself for most of the miscues.
Even teammates could see the toll it was taking on a man dubbed the NFL's next big thing.
It looked as if there was no way out of his funk Sunday.
Luck was working on a short week following an overtime loss at Carolina on Monday night, was still getting acclimated to a new play-caller and facing the NFL's top-ranked defense.
Somehow, Luck found his touch, eliminated the mistakes, shrugged off the doubters and turned those boos into cheers.
''All great quarterbacks have to have a case of amnesia,'' linebacker Robert Mathis said. ''It's extremely hard to do that, but that's why he's a franchise quarterback. There are not a lot of them out there. There aren't 32 of them, I can tell you that.''
Luck's numbers against Denver - 21 of 36 with 252 yards and two touchdowns - weren't spectacular, but he was sharper and more productive. And when the Colts needed him most, Luck delivered like the cornerstone quarterback Indy (4-5) needed.
Instead of digging out from another double-digit deficit, he led the Colts to a 17-0 second-quarter lead, their biggest of the season.
He finished the game with his usual scoring flurry, breaking two ties with back-to-back scores in the fourth quarter before finishing off the final six minutes with a little help from Denver's costly penalties.
''We all needed a win,'' he said. ''It was almost like a one-game playoff in a sense.''
Nobody needed it more than Luck, who has spent the past month dealing with questions and criticism.
Luck still has the second-most interceptions (12) in the NFL and his rating is still No. 31 among qualified starters.
With stats such as that, the outsiders questioned whether Luck was healthy, whether the Colts were hiding injuries, whether he should be benched, whether he had regressed and even if the Colts should make a midseason coaching change.
Along the way, Luck blamed himself for the mistakes and the losses.
But Sunday's resurgence could change everything.
The re-energized AFC South leaders are heading into their bye week with a boost of confidence and a blueprint for how to play the rest of this season.
''Instead of getting down, we go down and score first. That's a big part of it, that sets a tone,'' receiver Andre Johnson said. ''I think we set the tone in that game.''
If they keep it up, the two-time division champs could take advantage of a favorable schedule to earn a third straight division title and even build momentum heading into the playoffs.
Only two of their final seven games - Atlanta (6-3) and Pittsburgh (5-4) - come against teams with more than three wins.
''It's nice to walk out with a smile in any situation, especially after a losing streak,'' tight end Coby Fleener said.
Notes: Colts defensive lineman Henry Anderson will undergo surgery in the next couple of weeks to repair a sprained right knee, coach Chuck Pagano said. Anderson was placed on season-ending injured reserve earlier in the day. ... Pagano said Pro Bowl safety Mike Adams was still having his injured left ankle evaluated. Adams was injured in the first half Sunday after picking off a deflected ball for the first of Peyton Manning's two interceptions. ... Allen said he was suffering no lingering effects after he was poked in the eye by Broncos cornerback Aqib Talib with about two minutes left in Sunday's game.
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