The whole game was decided on the Harrison TD at the end of the first half... If the Cardinals just manage a FG there, they win. Hell, if Fitzgerald just makes the tackle at the half inch line they'd have won.
Actually because of the 15 yard personal foul on Arizona on the play, the Steelers would have got half the distance to the goal and the half can't end on a defensive penalty so they Steelers would have had one play to score from the foot line. So it wasn't quite as simple as "if Fitzgerald just makes the tackle".