Week 15 of the NFL season features a Saturday double-header. The second game is a primetime AFC West showdown between the Los Angeles Chargers and Kansas City Chiefs -- a matchup with huge playoff implications.

The Chargers are one-point favorites after opening as one-point underdogs. The Over-Under, or total number of points Vegas thinks will be scored, is 47, up one from the opener. The Chargers are -115 on the money line, meaning a $115 bet would return $100.

With so much at stake and the line swinging from side to side, you need to hear what SportsLine expert Mike Tierney has to say.

A veteran sportswriter with decades of experience covering the NFL, Tierney studies matchups like nobody else, and he's used his expertise to crush NFL picks.

After yet another cash on last week's game between the Saints and Falcons, he's now an insane 47-21 on NFL Over-Under picks since the start of last season. He's also hitting those picks 69 percent of the time in primetime matchups and is a blistering 7-1 on Over-Under picks involving the Chiefs.

And anybody who has been following his selections is way, way up.

Now, Tierney has analyzed every matchup, every trend, and every angle for Chiefs-Chargers and locked in his picks.

Tierney knows these teams are loaded with offensive weapons. The Chargers, winners of four straight, have averaged an impressive 32.8 points per game during that span. QB Philip Rivers, RB Melvin Gordon and WR Keenan Allen comprise one of the most dangerous offensive trios in the league.

The Chiefs are no stranger to the end zone either. Led by QB Alex Smith, RB Kareem Hunt, WR Tyreek Hill and TE Travis Kelce, Kansas City is sixth in the league in both total and scoring offense. 

Last week, Kansas City committed to Hunt and the run game in a decisive 26-15 victory over Oakland. Hunt had 25 carries, the second-most of the season, and 116 yards. He also found the end zone for the first time since Week 3.

But just because these two teams know how to light up a scoreboard doesn't mean this game is going Over 47.

K.C.'s offense has slowed in recent weeks as they've lost four of the last five. During that span, they've had some offensive clunkers, including a 10-point performance against the Bills and a nine-point disaster against the Giants.

The Chargers, meanwhile, have been playing at an extremely high level defensively. Seven of their last eight games have hit the Under as Los Angeles, led by fierce defensive end Joey Bosa (11.5 sacks), has become one of the better defensive squads in the league. 

The Chargers are second in points allowed at 17.3 per game and third against the pass at 200.3 yards per game. They've held their last three opponents - the Cowboys, Browns, and Redskins - to a combined 29 points.

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

He has isolated alarming stats that have led him to make a strong pick on one side of the total. He's sharing it all only over at SportsLine.

So which side of the total should you back in Chargers-Chiefs in this Saturday evening showdown? Visit SportsLine now to see what alarming stats determine whether Chiefs-Chargers goes Over or Under, all from the expert who is an astonishing 47-21 on his NFL totals picks since the start of last season.