They became too predictable. After the 9 point lead they went mainly to their running game to try to run clock and ice the game. Honestly, if they make the FG it may have worked. But they didn't which opened the door.
The 2nd to last drive we just had Brown make a play. They were looking to open it back up a bit, but (like most rhythm offenses) they got our of rhythm when they went to the run game which opened the door for RG3's mistake and Brown's play. They had run those underneath slants much of the game, but this time we made a play.
Then the last drive you are going against a fired up defense, and the 1st down play was huge. Great coverage allowing Brown to make a play and get the sack. Then we just made some plays and won the game, but again, they were out of rhythm, some of that their own doing.
I also think the cumulative effect of getting hits on RG3 when we could paid off. I liked that we didn't take a lot of chances with blitzes and our front 4 did a decent enough job at times getting pressure. But a key was when we had opportunities to get hits on RG3 we did, all throughout the game. I think that had a bit of an effect on him down the stretch in the 4th quarter as well.