The winning kick was set up when the Cowboys tipped a Payton Manning pass that was intercepted by Sean Lee, who returned it 13 yards to the Colts' 36-yard line.
Buehler followed that up six plays later with the decisive field goal 8 minutes into the extra frame, and Dallas (4-8) picked up its third road win of the season.
Jon Kitna competed 18-of-26 passes for 167 yards and a touchdown and Tashard Choice gained 100 yards with a score on 19 carries for the Cowboys, who also got a key late TD reception from Jason Witten.
On defense, Dallas returned two Manning interceptions for touchdowns -- one by Lee and another by Orlando Scandrick.
Manning finished the game 36-of-48 passing for 365 yards and two touchdowns for the Colts (6-6), who fell a full game behind Jacksonville in the AFC South.