The San Francisco 49ers host the Los Angeles Rams on Thursday Night Football to open Week 3 of the NFL season.

The line already has seen plenty of movement. The Rams opened as 2.5-point favorites, but the line moved up to -3.

The over-under is a low 40, meaning Las Vegas thinks 40 total points will be scored. It opened at 42, but quickly dropped.

Before you make any bets on Rams-49ers, you'll want to hear what Mike 'Top Dog' Tierney has to say.

Tierney went a sizzling 22-9 on NFL over-unders last season. And he's gone an impressive 4-1 this season, including nailing the under on last week's Thursday night game between the Texans and Bengals.

Part of his success: He's full of inside information. He has reported from seven Super Bowls and is a well-known national sportswriter. Anyone who has followed his picks has been well-rewarded.

Tierney knows the 49ers are in the top 10 in yards allowed at 299.5 and their yield per snap is an impressive fourth.

Their offense is a different story. San Francisco has yet to score a touchdown and all four of kicker Robbie Gould's field goals have come from outside of 30 yards, so they're not even getting close to the end zone.

But just because the 49ers struggle offensively doesn't mean Thursday Night Football goes under, especially with a low total of 40.

Tierney knows Rams QB Jared Goff's passer rating of 103.2 is good for 11th best in the NFL. And the last time these two teams met, they put up 43 points. He also knows that Thursday Night Football starts at 5:30pm local time in the Bay Area, so the atmosphere at Levi's Stadium may not be as rowdy as normal. The Rams may have more success offensively than on a typical Sunday.

And the 49ers have showed promise on offense. They're averaging over 100 yards per game on the ground. They've played two above average defenses in the Panthers and Seahawks thus far. Now they get a defense coming off a short week and playing a road game.

Tierney is leaning on the Rams to cover the two-point spread, but what about the Over-Under, which he's made his name picking?

He knows there's a huge x-factor that ultimately determines whether Rams vs. 49ers on Thursday Night Football goes over or under. And he's sharing it over at SportsLine.

So which side should you back in 49ers-Rams on Thursday Night Football? And does this game go Over or Under? Visit SportsLine now to see what big x-factor sends 49ers-Rams Over or Under, and see which side of the total you need to be all over, all from the expert who is blistering hot in total plays.