Week 13 of the NFL season begins with a "Thursday Night Football" matchup between the division-rival Dallas Cowboys and Washington Redskins from AT&T Stadium. This isn't a short week for either team since both played on Thanksgiving and have had a full seven days to prepare.

The Redskins are favored by two points after the line opened with the Cowboys being favored by 1.5. The Over-Under, or total number of points Vegas thinks will be scored, is 46, up two from an open of 44.

Before you lock in your pick for Redskins-Cowboys on "Thursday Night Football," you need to see what SportsLine's Mike Tierney has to say.

In Week 10 when the Redskins hosted the Vikings as 1.5-point dogs, Tierney told readers to grab Minnesota without hesitation. The result: Vikes 38, Redskins 30 in a game that wasn't that close.

Amazingly, it was Tierney's seventh straight win picking Redskins games. Anyone who has followed his picks is way, way up.

Part of his success: No one knows the NFL like Tierney. A national sportswriter whose work appears in the New York Times and Los Angeles Times, he has reported from seven Super Bowls. And he knows what matters most in a bitter divisional rivalry game like this.

Tierney knows injuries are a major factor for both teams. The Cowboys could be very thin at linebacker. Sean Lee (hamstring) will sit out Thursday's game, his third in a row. In his absence, the Cowboys have been lit up for 27, 37 and 28 points. Justin Durant (concussion) is also out for Dallas and Anthony Hitchens (groin) is questionable.

Dallas has struggled offensively without suspended running back Ezekiel Elliott. Big D hasn't topped nine points during its three-game skid, and no running back or wide receiver has hit 100 yards.

But just because the Cowboys have stumbled doesn't mean they can't cover against a 5-6 Washington team.

The Redskins have plenty of injuries of their own. Tight end Jordan Reed (hamstring) hasn't seen the field since Week 8 and will sit once again Thursday night. Running back Chris Thompson (leg), who led Washington in receiving and rushing, is on injured reserve, and left tackle Trent Williams (knee) is questionable.

And the Cowboys beat the Redskins by 14 in Week 8 and have won seven of the last nine meetings outright.

SportsLine's advanced projection model is calling for Cowboys QB Dak Prescott to throw for over 200 yards and two touchdowns on Thursday. And Dallas' ground game has a date with a middle-of-the-road Redskins rush defense that's giving up 111 yards per game and allowed Mark Ingram to go off for 134 yards and a TD two weeks ago.

Tierney is leaning Under for "Thursday Night Football," but what about against the spread?

He knows there's an x-factor no one is thinking about that ultimately determines the point-spread winner for Redskins-Cowboys. And he's sharing it over at SportsLine.

So which side should you back in Redskins-Redskins on Thursday night? Visit SportsLine now to see what big x-factor determines which side of Redskins-Cowboys you need to be all over, all from the expert who has nailed his past seven Redskins picks, and find out.