The top overall pick completed 16 of 25 passes for 175 yards and added a 1-yard touchdown run for the Colts (1-1), who held their own against a perennial Super Bowl contender.
Ben Roethlisberger passed for 81 yards with a touchdown and an interception for the Steelers (1-1), who took an early 14-0 lead when Ike Taylor picked off Luck's pass and took it 50 yards for a score.
The pick hardly rattled Luck, who led the Colts to scores on three of their next four drives. By the time he left, Indianapolis (No. 32 in the AP Pro32) held a 17-14 at the break.
Rookie Danny Hrapmann kicked four second-half field goals for the Steelers, including the 22-yard winner with 23 seconds remaining.
Luck dazzled in his preseason debut last week against St. Louis, passing for a pair of touchdowns in a 38-3 romp. He expected a sterner test against the Steelers — who led the NFL in total defense for the fourth time in the last nine years in 2011 — and he got it.
Pittsburgh (No. 7) sent its first string defense — minus injured stars James Harrison and Casey Hampton — after Luck from the start. The Colts managed just one first down on their first three possessions, the third one ending with Luck underthrowing Reggie Wayne on a sideline pattern that Taylor stepped in front of and took down the sideline for a touchdown.
"I turned around and the ball was right there," Taylor said. "I just had to make sure I caught it."
Things appeared to get worse for Luck on Indianapolis' next play, when he was sacked by LaMarr Woodley.
No biggie. Showing the poise that made the Colts choose him to be the heir apparent to Peyton Manning, Luck led a 10-play, 80-yard drive that ended with Donald Brown's 1-yard plunge.
Luck had it going again on Indianapolis' next possession only to be undone but a bit of bad, well, luck. He hit rookie wide receiver T.Y. Hilton in stride down the middle only to have the wide-open Hilton throw the ball up in the air. Pittsburgh's Cortez Allen ran underneath it to thwart the drive, but it hardly slowed the Colts.
Indianapolis tied it at 14 when Luck deftly slid into the end zone on fourth-and-goal from the 1, ending a drive in which Luck completed all five of his passes.
Luck got one more chance just before the half, and he made it count. Working exclusively out of the shotgun, Luck led the Colts 31 yards in five plays, giving Adam Vinatieri just enough time — and room — to sneak a 53-yard field goal between the uprights at the gun.
"It showed character and maturity of Andrew to come back, make plays, move the ball down the field and have two nice drives," Indianapolis coach Chuck Pagano said.
The Steelers aren't in the midst of a rebuilding process like the Colts, but they are trying to get comfortable with new offensive coordinator Todd Haley's system. The results, so far, are mixed.
Roethlisberger completed 7 of 8 passes during his one drive of work in the opener against Philadelphia last week, all of them quick hitters. His first pass Sunday night ended up in the hands of Indianapolis' Antoine Bethea when the safety cut in front of a pass intended for Pittsburgh wide receiver Antonio Brown.
Antonio Brown and Roethlisberger atoned the next time the Steelers had the ball, with Brown doing most of the work. He hauled in an 18-yard pass from Roethlisberger on third-and-11 to extend the drive then put together a highlight-reel 57 yard catch-and-run for a touchdown.
The play was all Brown. He took a screen pass from Roethlisberger, cut up the field and used some great downfield blocking by running back Baron Batch to get to the end zone. Brown — who has become Roethlisberger's favorite target with Mike Wallace in the midst of a holdout — added some style points by doing a forward flip as he crossed the goal line.
Roethlisberger stayed out for one more series, throwing a pair of incompletions before giving way to veteran backup Charlie Batch.
NOTES: Colts DE Robert Mathis left the game in the first quarter with a shoulder strain and did not return. Indianapolis WR Austin Collie underwent a concussion test after taking a blow to the head from Pittsburgh linebacker Larry Foote. ... The Steelers travel to Buffalo on Saturday night while the Colts visit Washington. ... Harrison, Hampton, running backs Isaac Redman and Rashard Mendenhall and linebacker Jason Worilds did not dress for the Steelers. ... Indianapolis backup QB Drew Stanton completed 4 of 13 passes for 69 yards and a touchdown.
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