The Cardinals stymied the Rams on the first possession of overtime, and St. Louis punter Donnie Jones booted a 54-yarder to Peterson, who fielded it on the Arizona 1-yard line.
Peterson opted to run up the middle and then veered to the right sideline after breaking a pair of tackles and sprinted into the end zone for the dramatic game-winner.
The Rams (1-7) lost despite the return of Sam Bradford, who came back from a sprained ankle to throw for 255 yards and an interception.
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