I think the Broncos came out thinking an easy victory vs. a winless (until now) team. IOW, they "played down," always a dangerous attitude going into any game. But, altho pros, these are young guys; so were the Giants. The Giants decided to make a statement; the Broncos didn't. 

Most noteworthy is that the Giants' D outplayed the Denver D. They completely shut down the Denver running game, a staple of the Denver O. Denver's QBs shine only when the running game is working. Who's to blame? The entire team! Christ, McManus missed 2 easy field goals for god's sake.

I hope this loss was good for the Broncos. Maybe now they've got it out of their system. I hope!!