San Francisco 49ers at Los Angeles Chargers: Keys to upset

CARSON – Here comes Game 1 of 13 without Jimmy Garoppolo to finish off the 49ers season.

Finish? That’s definitely not the word the 49ers invoked in their locker room, no matter how demoralized they were losing their star quarterback to a season-ending knee injury last Sunday.

“There’s a lot of people out there doubting us and counting us out,” said C.J. Beathard, Garoppolo’s predecessor and now replacement.

“Everybody in the building is excited,” Beathard added, “and we’re ready to get rolling and win some games moving forward.”

The 49ers (1-2) roll in Sunday to the quaint, temporary home of the Chargers (1-2) at Carson’s StubHub Center (capacity: 25,386).

Beathard called it “crazy” that, of all teams, he’ll be facing the Chargers, a team he grew up rooting for because their general manager was his grandfather, Bobby, a Pro Football Hall of Fame inductee this year.

Here are five ways the 49ers can pull off a crazy upset:

1. BIG-PLAY BREIDA: Running back Matt Breida shares the NFL rushing lead (with Dallas’ Ezekiel Elliott; 274 yards) in large part because of a big-play ability. Rushing yards should be harder to come by now that defenses will be daring Beathard to air it out and prove he’s as capable as Garoppolo.

But Breida isn’t just lucking into a NFL-best 8.6 yards per carry, with a league-high six carries of 20-plus yards. He credited his blockers, then explained why his vision is as impressive as his cut-back ability and speed.

“Once I get to that second level, the field just opens up and I feel if I see green grass, I’m going to hit it,” Breida said. “Of course, my speed helps me.”

Chargers coach Anthony Lynn called Breida “a classic zone runner” who’s flourishing under running backs coach Bobby Turner. Breida splits time with Alfred Morris, but both are battling knee injuries from last game, and their run threat is vital to help Beathard’s re-entry at QB.

2. DON’T BE BALLHOG: Beathard’s tendency to hold onto the ball so long in the pocket resulted in him taking punishing hits last season (19 sacks, 63 hits, 5 1/2 games). That needs to change. But can it if receivers aren’t getting open?

Garoppolo’s pocket courage saw him get sacked 13 times as receivers struggled. Coach Kyle Shanahan said the Lions and Chiefs frequently held receivers and it’s a tactic that generally succeeded, aside from a defensive holding call on the Lions that nullified a would-be interception.

Shanahan’s wily schemes will need to create mismatches more than ever against a susceptible defense.

Marquise Goodwin’s Week 1 quadriceps injury is looking better, so that could boost the offense. And Beathard surely will turn often to his former Iowa teammate George Kittle, whose 191 receiving yards are sixth-most among tight ends.

3. THIRD-DOWN STOPS: Through Philip Rivers’ film study, he’s seen a 49ers defense that’s allowing way too many third-down conversions: 7-of-17 by the Vikings, 7-of-16 by the Lions and 7-of-11 by the Chiefs. That’s an average of 47.7-percent, and while it’s fifth-worst in the NFL, at least the Chargers defense is one notch lower (48.6 percent).

Defensive coordinator Robert Saleh pointed to multiple breakdowns on third down as to why the Chiefs scored five touchdowns on five series before halftime.

“It comes down to tackling and third down,” Saleh said. “It is that simple, because if we take care of those third-and-long situations, as a defensive unit, coaches included, I feel like there’s three field goals and a non-touchdown and the outlook is a completely different deal.”

Instead, the 49ers made the Chiefs look “all-world,” as Saleh said, behind young quarterback Patrick Mahomes. Well, next up is the NFL’s fifth-oldest QB.

4. RIVERS EDGE: Once Rivers passes for 222 yards on Sunday, he’ll move past John Elway at No. 8 among the NFL’s all-time passing yards leaders with 51,476 yards. Rivers, 36, is in his 15th season. Beathard, 24, in making his sixth career start, with 1,430 yards to his name as a rookie last year.

Lynn says Rivers looks as spry as ever, stating: “His age is not even a factor the way he runs around and the way he slings the ball. He prepares like a winner and that’s where it all starts.”

Rivers is 3-0 all-time against the 49ers with nine touchdowns, three interceptions and a 108.1 passer rating. He’s also been sacked only three times in those three games. This would be a good time for the 49ers pass rush to show up, and that means DeForest Buckner (3 1/2 sacks) is in high demand.

5. SAFETY COMPARISON: Strong safety Jaquiski Tartt likely will miss a second straight game with a shoulder stinger, and free safety Adrian Colbert is coping with a hip injury that forced him out last game. Rivers will be sure to throw deep to test them or their potential replacements, Antone Exum, D.J. Reid or Tyvis Powell.

Whoever plays safety better be ready to help a struggling cornerback corps that’s missing Richard Sherman (calf strain). Jimmie Ward and Ahkello Witherspoon are the projected starters, with rookie Tarvarius Moore in the mix and K’Waun Williams in the slot.

Key stat: no interceptions through three games by the 49ers.

On the other side, Chargers rookie safety Derwin James was coveted by the 49ers in the draft but they passed on him to take right tackle Mike McGlinchey. James’ athletic ability and range lets him play various spots, including as a blitzer against running backs and tight ends.

Said Lynn: “He’s doing really well. But he’s a young guy, still learning. He’s a baby. He’s going to be a heck of a player in this league for a long time.”