Cruz, who signed a five-year contract extension with the Giants last month, reeled in the TD pass in the first quarter, giving New York a 10-3 lead.
Manning finished 2-of-5 through the air for 73 yards while David Wilson gained 16 rushing yards on five carries.
Pittsburgh's Ben Roethlisberger picked up 36 passing yards on 4-of-8 efficiency.
LaRod Stephens-Howling led the Steelers' ground game, gaining 40 yards on seven carries.
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