Dispense with the defensive (the irony in that is it was something you couldn't play) insults because it just makes you look foolish. YOU stepped off the gas. That is YOUR fault. If I get up big on an opponent I always do the sportsman like thing and just keep running the ball. However, once they get it back, they are trying to score. There's no reason you should let off the gas and let them back into the game on defense.
Look, I get tired of people coming on here and complaining year after year about "the CPU cheating for a win" or some "hidden momentum or handicap to make me lose". They are all just excuses for your loss. As you said, he ran TWO plays. I don't even care if your guys weren't "guarding them as they were earlier in the game". You control a defender on the defense. It shouldn't be hard to read and react or at least chose a play that targets the side of the field where he likes to go.
People these days just refuse to adjust to their opponent, and when they don't get a win handed to them on a silver platter they complain about how the CPU has it out for them or something stupid like that. Just step your game up and learn from the loss.