The Cards may have one of the best defenses in the league and their game was won because of the two turnovers (Brady's INT and the blocked punt which gave them 10 point moving the ball a total of 10 yards). Otherwise, they wouldn't have scored more than 10 points.
I don't think Denver is nearly as good as you make them. Manning hasn't been Manning no matter how much the media wants to convince us he is. The Pats could lose, but I don't think Manning is nearly as scary as you make him. And you can definitely score points on their defense (25th in points allowed per game).