INDIANAPOLIS - Without question Lucas Oil Stadium's retractable roof, which can close and open in 10 minutes, and its largest movable window wall in the world, open Sunday night, make it an architectural work to behold.

But for all the innovations inside the $720 million structure, the Bears always will remember it as the place they finally found the magical switch for 2008 they couldn't find for six long, frustrating weeks of preseason.

Consider it flipped.

The defense played with a purpose and passion that had been only a summer rumor and, thanks to silky rookie Matt Forte, the offense finally provided results in the running game to match Lovie Smith's

rhetoric.

Which team playing in the Indiana capital Sunday night was a Super Bowl contender, and which one was considered an underachiever on its way to a sub-.500 season?

In a stunning 29-13 victory over the Colts, the Bears made one of the louder statements of the opening weekend of the NFL season.

Using fourth-down stops and fumble returns for touchdowns as exclamation points and key runs by Forte behind a resurgent offensive line as italic letters, it said, "We're back!"

Who knew?

The Bears will say they did and scold naysayers for writing them off before the first regular-season kickoff. But even the most optimistic of Bears would have to admit surprising themselves against a Colts team many considered one of the AFC's best.

The worst defense in the NFL during exhibition season didn't resemble the unit the Colts remembered from Super Bowl XLI. It looked better. Nastier. More focused and opportunistic.

By the time Lance Briggs scooped up a fumble caused when Charles Tillman stripped Marvin Harrison and returned it 21 yards for a touchdown, the Bears' defense had earned back the benefit of the doubt it had lost after last season's debacle.

But the sense of urgency that was missing since players reported to Bourbonnais surfaced on the first series. They mixed in a variety of blitzes to make the Colts' Peyton Manning take as much time as the Bears hoped to develop a rhythm.

Holes closed quickly, blocks were shed cleanly, and suddenly the defense bad enough against the run in the exhibition season to have to defend the validity of the Cover-2 was stopping the run.

When Adewale Ogunleye tackled Joseph Addai in the end zone for a safety in the second quarter, it was obvious the defense the Bears kept promising would show up had shown up.

Sure, it helped that the Colts oddly ignored any attempt to establish a ground game in the first half, throwing 20 times compared to 10 runs. But credit the Bears for forcing input in those decisions.

Uncharacteristically, the Bears' defense helped bail out the special teams more than the offense.

Devin Hester indeed had an impact on the game, but not the way the Bears had hoped. The Colts successfully kicked away from Hester in the first half by using line drives and squibs. But to start the second half, Adam Vinatieri booted one directly to Hester 7 yards deep in the end zone. Hester caught the ball and appeared ready to take a touchback when at the last second he decided to run it out.

It was the Bears' first dumb decision of the game. The Colts swarmed Hester at the 3, and all of a sudden the Bears were pinned deep in their own territory, the crowd was back in the game, and the Colts had momentum they had struggled to maintain.

On the next series, on cue, Manning steered the Colts into the end zone for the first time, culminating the drive with a 6-yard TD pass to Reggie Wayne.

It may get lost in all the other highlights, but credit efficient Kyle Orton and the offense for the buzz kill they provided when the Bears got the ball back with the place rocking. The Bears didn't score on that drive but ran 12 plays and ate 7 minutes, 12 seconds off the clock before punting it back to the Colts. It was one of the most clutch efforts of the night for the offense.

Having a bona fide NFL running back, which the Bears have lacked since trading Thomas Jones, makes such drives possible.

Forte made history with 100 yards in the first half, and he will have few runs any more important than his 50-yarder for a TD with 4:59 left in the first quarter. More than any other play, that provided early confirmation that the Bears might be capable of pulling off the upset only they thought was possible.

Jerry Angelo always was reluctant to use the word "special" to describe Anthony Thomas, the last rookie running back to make such an impact. So get out your football thesaurus to find another adjective for Forte in case Angelo thinks it's too early: exceptional, reliable, outstanding.

Finding words to describe what the Bears did here Sunday night proved more challenging. You just had to see what maybe only the Bears believed was possible.