David Eulitt / Stringer

KANSAS CITY — The 49ers lost, 38-27, Sunday afternoon at Kansas City to fall to 1-2 on the season. This game was marked by drastic lows and highs, with the 49ers digging themselves into too massive of a hole to prevail on the right side. Unfortunately for the 49ers, Sunday’s result takes a backseat to Jimmy Garoppolo’s left knee injury, which is feared to be a torn ACL, in precedence.

Here are five thoughts from Sunday’s game.

1. Garoppolo’s health is the biggest concern.

That much is obvious. Kyle Shanahan and the 49ers fear Garoppolo tore his left ACL, though they won’t know — or won’t disclose the injury’s specifics— until at least Monday.

If it’s true, the vision for a highly hopeful 49ers season changes drastically.

Garoppolo hurt his left knee and was carted off the field during the fourth quarter. It initially appeared Garoppolo was injured when he slammed into Chiefs defensive back Steven Nelson right after his knee buckled. Instead of running out of bounds, Garoppolo fought for extra yardage. He hunched over for a couple minutes on the sideline, then sauntered to the blue medical tent alongside a couple 49ers staffers.

Garoppolo’s injury headlines a laundry list of injuries that hampered the 49ers all game long.

Richard Sherman (calf) and Adrian Colbert (hip) suffered injuries in the first half that sidelined them for the rest of the game. Matt Breida hurt his knee on a non-contact injury, but he returned and produced 90 yards on 10 carries.

In the second half, Jimmie Ward left the game with cramping, Foster got the wind knocked out of him, and Solomon Thomas was hurt on a collision. Mike Person briefly exited the contest.

The vast majority of these injuries is considered to be minor. But the most important one, Garoppolo’s, is not.

2. Credit the 49ers for fighting back.

The Chiefs led by 25 points entering halftime, and they received the ball to start the second half, but the 49ers got consecutive defensive stops and followed them with touchdown drives.

As ugly as the first half was — it was likely the worst in Kyle Shanahan’s 19 games as the 49ers head coach — they scored 18 straight points to cut the Kansas City lead to 11 points with nearly 18 minutes remaining. Shanahan put on a play-calling clinic, calling play-actions, shovel passes, and even fullback options, all of which the offense executed. The 49ers needed to play a perfect half to have a chance, and for the majority of the second half, they were on track.

Then Garoppolo got hurt, and everything tailspun. C.J. Beathard entered the game and connected with George Kittle for a touchdown, but Kyle Juszczyk was flagged for pass interference. The 49ers settled for a field goal with five minutes remaining to cut the lead to 11. Time wasn’t on their side.

3. The defense was a mess.

This was never a great matchup for the 49ers defense, which crumbled in the fourth quarter of their win last Sunday. Patrick Mahomes led the NFL’s most prolific offense into Sunday’s matchup, and for the first half, they resembled every bit of that.

The Chiefs scored touchdowns on their each of their first five drives.

Anything they wanted, they got. The running game worked, Travis Kelce operated in the intermediate passing game, and Tyreek Hill stretched the defense. Even when Mahomes had nowhere to go, he found success. On his second touchdown, he scrambled backwards about 15 yards before fitting a touchdown throw in between several 49ers defenders. He posted 252 yards and three touchdowns in the first half alone.

There were coverage issues. There were tackling issues. There were communication issues. The pass rush was virtually nonexistent. The 49ers allowed the Chiefs to convert four of their five third-down opportunities in the first half.

Their defense is built on physicality and length, contrasting Kansas City’s fast, spread-it-out offensive attack. The latter prevailed in a big way.

4. Untimely penalties continue to kick the 49ers.

They committed nine penalties for 106 yards in the first half and 14 flags for 147 yards altogether. In this environment, against this team, they needed to play as close to mistake-free football as possible. But they continued to kick themselves, allowing the Chiefs to extend drives.

Two untimely penalties thwarted any possibility for a memorable comeback. The first was Juszczyk’s offensive pass interference. The second was Ahkello Witherspoon’s defensive pass interference flag on Kansas City’s final drive, which solidified the result. It was a fitting way to watch the 49ers bow out, with Witherspoon, who didn’t start the game, making a mental mistake at the worst time.

5. The 49ers haven’t played a full 60 minutes yet.

Week 1 featured a slow start. The 49ers had to overcome an 18-point deficit to give themselves a chance at Minnesota, which they did in the fourth quarter, but it came too late. Last week, the 49ers went up by 17 points, only to surrender touchdown drives of 80 and 79 yards to the Detroit Lions in the fourth quarter, cutting the lead to three points. San Francisco held on.

Sunday was more of the same. These are growing pains for a young team still in the middle of a rebuild, which may last longer than expected if the diagnosis on Garoppolo’s knee is as severe as most think.