Cruz is no longer a newcomer. He is the Giants' second-leading receiver in terms of catches (28) and yards (497), and leads the team in receiving touchdowns (4). He makes contested catches, breaks tackles, and gains chunks of yardage, at a rate of 17.8 yards per catch. He has proven capable of playing any receiver position, but is at his best in the slot.
Both Dolphins safeties worked to the outside, to help on the outside receivers, leaving Cruz alone in the middle against Allen. The matchup wasn't fair for Allen, as he isn't as quick as Cruz, and he had a lot of open space to cover.
Manning was looking to Cruz all the way and Cruz beat Allen badly to the inside. Thanks to the maximum protection, Manning had the necessary time to make an accurate deep throw for the winning score in a tight contest.