In the first quarter Sunday, Kansas City wide receiver Sammy Watkins took a handoff on a jet sweep, ran through an arm tackle by 49ers defensive tackle Solomon Thomas, avoided a diving tackle attempt by inside linebacker Reuben Foster and finished his 11-yard scamper by eluding an arm tackle by defensive tackle by Sheldon Day.

Then, in the second quarter, Watkins caught a slant at the 10-yard line, broke through inside linebacker Fred Warner’s arm tackle, did the same to safety D.J. Reed and bowled over cornerback Jimmie Ward at the goal line to cap a 12-yard touchdown reception.

Yes, Watkins is good, but here’s the takeaway: The 49ers can’t tackle.

OK, that’s a bit harsh, but this is accurate: The 49ers are the worst-tackling team in the NFL through the season’s first three games.

The 49ers have a league-high 43 missed tackles, according to Pro Football Focus, and there’s no sign of improvement after they whiffed on 17 in a 38-27 loss to the Chiefs.

This week, after discussion of the injury that brought them to their knees (quarterback Jimmy Garoppolo’s torn ACL), the second-most popular topic has been the 49ers’ inability to bring ball-carriers to the ground.

Sunday’s game Who: 49ers (1-2) at L.A. Chargers (1-2) When: 1:25 p.m. Where: Carson, Los Angeles County TV:Channel: 5Channel: 13Channel: 46 Radio: 810, 107.7

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On Wednesday, head coach Kyle Shanahan was asked about the issues with a defense that ranks 23rd in yards allowed per game (384.7) and 27th in points per game (29.7).

“I think the most obvious one is we’ve got to tackle better,” Shanahan said. “I think you guy can see that statistically. You can see it with your own eyes just watching the game.”

On Thursday, defensive coordinator Robert Saleh struck the same note when asked about a first-half performance in which the 49ers surrendered touchdowns on all five K.C. possessions.

“It’s going to sound very elementary, but it comes down to obviously, tackling, which needs to get better,” Saleh said. “It’s not very good, obviously.”

So what’s the improvement plan entering Sunday’s road game against the Chargers, who boast Pro Bowl quarterback Philip Rivers and the NFL’s fifth-ranked offense (415.3 yards per game)?

For starters, on Wednesday the 49ers went through a specific tackling drill during a non-padded practice that had been reserved for padded sessions. Last week, Saleh said the defense’s biggest problem was taking poor angles. This week, he highlighted shoddy fundamentals.

“It’s very clear when you turn on the tape that we’re actually lunging and ducking our heads at the point of attack,” Saleh said. “When you teach tackling, everything that we talk about is you’ve got to run your body through their body. ... Somewhere along the line, there’s a disconnect. And so, as coaches, we’ve got to do a better job getting that message across.”

The tackling troubles figured to lessen last Sunday with the return of Foster, who served a season-opening, two-game suspension. However, Foster became a huge part of the problem: He finished with seven tackles and six missed tackles, according to Pro Football Focus.

Foster’s assessment of his performance: “That’s uncalled for,” he said.

Saleh no doubt feels the same about the entire defense’s performance.

Since he was hired last year, Saleh repeatedly has said he wants his defense to be known for an “all gas, no brakes” mentality and “extreme violence.”

Instead, after three games this season, the 49ers’ defense is best known for an extreme inability to perform one of football’s fundamentals.

“We’re lunging at the point of attack and that’s what’s leading to all of those arm tackles and missed tackles,” Saleh said. “So hopefully, we’ve got a good bead on it. It was very evident last week versus the Chiefs and we’ll get it taught and, hopefully, have good results.”

Eric Branch is a San Francisco Chronicle staff writer. Email: ebranch@sfchronicle.com Twitter: @Eric_Branch