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This loss was fairly simple: the 49ers could move the ball, but they couldn’t hold onto it.

And after two weeks of improvement on special teams, they also posted yet another atrocious performance in that phase of the game, so even a relatively explosive second half from their offense couldn’t overcome the weight of many miscues.

The Jacksonville Jaguars held on to beat the 49ers, 26-21, who must wash the stench of Sunday away quickly with a Thursday night showdown against the Los Angeles Rams looming.

“We can’t let one [loss] become two,” 49ers coach Kyle Shanahan said afterward. “We have another game here in four days.”

To their credit, the 49ers didn’t collapse under the weight of their errors — even though that seemed very possible late in the first half. The defense gave up 107 yards to Jacksonville on one touchdown drive alone (thanks to penalties that allowed the Jaguars to gain more) and the offense went three-and-out instead of rebutting.

At that point, with the Jaguars holding the ball and leading 14-3, it looked like the game might turn into a blowout. But coordinator Robert Saleh’s defense stiffened up, doing its part to give the 49ers offense repeated chances — many of which they blew down the stretch.

In fact, the defense allowed only 94 yards on 29 plays after halftime — 3.2 yards per play — after being roughhoused to the tune of 231 yards on 6.8 yards per play before the break.

It ended as a respectable performance in the first game without injured defensive end Nick Bosa. That was certainly a credit to Saleh, whose unit struggled to pressure Jacksonville quarterback Trevor Lawrence. The 49ers did so on only four of his 31 drop backs.

When the 49ers did finally manufacture some heat, Lawrence nearly coughed up Jacksonville’s advantage. Rookie 49ers defensive back Upton Stout intercepted Lawrence, but the play was nullified by an illegal contact penalty that the 49ers vehemently disagreed with.

“That call on Upton, that was egregious, man,” 49ers defensive end Sam Okuayinonu said in the locker room. “But that’s football. You’ve got to roll with the punches.”

And the 49ers did a decidedly poor job of that. In the first half, tight end Luke Farrell — who previously played for Jacksonville —fumbled away an early-game advantage. Over the next three quarters, Kendrick Bourne, Jauan Jennings and Christian McCaffrey each dropped critical passes. The one to McCaffrey bounced for an interception to Jaguars linebacker Devin Lloyd.

“I can make that play and I need to make that play,” McCaffrey said.

In the second half, 49ers quarterback Brock Purdy threw another interception — and although this ball was tipped at the line, it appeared to have been headed into an unnecessarily risky window on first down.

Ultimately, Jacksonville collected four takeaways (they lead the NFL with 13) while the 49ers — although they came close with Stout’s nullified play and two near-picks from linebacker Fred Warner — couldn’t collect any. They still don’t have an interception this season.

“We took too long to get going — that first half was not good enough,” Warner said, citing a long touchdown run from Jacksonville running back Travis Etienne Jr. “The explosive runs, leaky yardage. I think in the second half it was better, but still not up to our standard.”

There were some postgame fireworks when Jaguars head coach Liam Coen yelled at Saleh on the field, ostensibly in reaction to the defensive coordinator’s pointed comments about Jacksonville’s “legal signal stealing system” this week.

“I don’t think he should be that sensitive about it,” Shanahan said of Coen after the game. “But it is what it is. I’m not too worried about it.”

Shanahan must instead turn his focus to the 3-1 Rams, who were 27-20 victors over the previously undefeated Indianapolis Colts on Sunday.

The 49ers’ injury concerns continued mounting during this loss. Jennings, who played through an ankle issue, worked in clear discomfort after taking a brutal shot to the ribs on a two-point conversion. Second-year standout Ricky Pearsall exited the game shortly after feeling discomfort in his knee.

“I fell pretty hard on my knee,” Pearsall said. “I was feeling pain and instability, so I wasn’t trying to mess with it…I just kind of shut it down from there.”

Pearsall had gotten off to a spectacular start, hauling in four catches including a sensational 31-yard deep grab from Purdy. Without Pearsall, the 49ers again strained through McCaffrey — who saw limited running room but caught six passes for 92 yards — and a jumble of smaller contributions from other options.

It’s especially clear that the 49ers are missing do-everything tight end George Kittle, who must spend at least one more game on injured reserve as he recovers from a strained hamstring.

Without Kittle, the 49ers’ margins will remain thin — and almost certainly too thin to overcome Sunday’s catastrophic level of play on special teams.

It’s increasingly remarkable that the 49ers managed to eke out a Week 1 win over the Seattle Seahawks despite the massive struggles of their kicking game. They weren’t so fortunate against the Jaguars, who notched two long returns — including an 87-yard punt return for touchdown by Parker Washington.

That proved to be the difference in this game. But it was far from the only swing play. The 49ers departed Levi’s Stadium knowing that their sloppiness had left several game-turning opportunities on the table — including a final one that was extinguished by a strip-sack from former 49ers defensive lineman Arik Armstead.

“We made a bunch of mistakes all over the field and still had a chance to win,” McCaffrey said. “With an early game coming up, you just correct these mistakes. A lot of them are super uncharacteristic and we’ve got to just look ourselves in the mirror and move on.

“I’ve never part of an undefeated team. When you lose, it’s about how you respond…The beauty is that we play in four days.”