Willie Parker rushed for 59 yards; Hines Ward caught three passes for 68 yards; and Antwaan Randle El and Heath Miller had touchdown catches for the Steelers, who travel to Denver for next Sunday's AFC title game.
A late drive ended on a fumble by Pittsburgh's Jerome Bettis at the two yard-line with 1:20 left in the game, and the Steelers driving for a game-clinching touchdown. Roethlisberger made a game-saving tackle on Colts cornerback Nick Harper, who recovered Bettis' fumble and appeared headed for a touchdown.
The Colts' Mike Vanderjagt badly missed a 46-yard field goal attempt in the final seconds.
Peyton Manning was 22-for-38 for 290 yards, one touchdown and no interceptions for the Colts, who had a disappointing ending after beginning the season with 13 consecutive wins.