Among the gaffes: a fake field goal from the New York 3 early in the fourth quarter on which kicker Shaun Suisham lost a yard. That wasted a 63-yard punt return by Sanders on his first such runback all season.
Eli Manning threw for only 125 yards in one of the worst games of his career.
Back immediately came the Giants, helped by a 41-yard interference call on Lewis. Andre Brown powered in from the 1 a play after Pittsburgh safety Ryan Clark's late hit on Cruz in the end zone gave New York a first down.
Then Umenyiora and Boley made their huge play.
Lewis wasn't through contributing to New York's yardage. He also had a 46-yard interference penalty guarding Cruz, but Lawrence Tynes' field goal try was short from 51 yards. In the final 31 seconds of the half, Roethlisberger hit Jerricho Cotchery for 24 yards, Heath Miller for 23, and Suisham nailed a 30-yard field goal.
Tynes matched that with a 50-yarder in the third quarter set up by Martellus Bennett's 33-yard reception. Tynes later made a 23-yarder for a 20-10 lead.
Wallace's weaving dash across half the field for a 51-yard score that made it 20-17.