McCarthy's conservative playcalling on the road will keep the Commanders in the game longer than they should be. And if the game is close heading into the 4th quarter, then anything can happen...and bad things tend to happen on the road for this team (penalties, mistakes, etc.). They have a hard time handling the crowd noise and such, mental misfits in some games.
Plus, Quinn may come out in the old bend-but-don't-break defense, not forcing the Commanders to pass...allowing chunk run yardage on 1st downs and quick short passes, which may give Washington the chance to move the ball all the way down the field...and then the Cowboys will be in TD-prevention mode in the Red Zone (which would be their win).
So, between McCarthy and Quinn, their lack of urgency early could and likely will keep Washington in the game.
I still don't trust this coaching staff to have a killer instinct early.
If the Cowboys defense is able to get an early turnover (punch out, stripped sack, or something), then the Cowboys may get rolling...otherwise, I expect a close game against this division rival, especially since it will be their Superbowl this season.