HOUSTON — Chargers running back Amar Johnson doesn’t have a ton of NFL experience, but he knows to make every moment count.

“You don’t get the most opportunities at practice, so you’ve got to maximize the opportunities that you do get,” said Johnson, who had two touchdowns and a successful conversion run Thursday in a 27-7 victory over the Houston Texans in a preseason opener.

“Every game you kind of hit the reset button like, yeah, I did something this week, but the next game is a new week.”

Jim Harbaugh said the urgency is palpable, especially for players looking to secure one of the last few roster spots.

“That’s why you play like your football life is at stake,” the Chargers coach said. “Because it kind of is.”

Johnson had a seven-yard touchdown run in the first half, then turned a short reception into a 55-yard gain in the second. He was tackled a yard short of the end zone. He smiled when asked about that, knowing he likely was going to take a ribbing from teammates.

“I had to punch it in one more time,” he said. And he did, scoring from the one on the following play.

Chargers running back Amar Johnson runs past Houston Texans cornerback Brandon Codrington after a catch during a preseason game on Thursday.

(David J. Phillip / Associated Press)

Starting running back Omarion Hampton and most of the starters watched from the sideline for the Chargers, who got a reminder last year of how important it is to have depth. Injuries turned the position into a revolving door last fall.

Getting the ground game going is a staple of new offensive coordinator Mike McDaniel. The Chargers haven’t had a 1,000-yard rusher since Melvin Gordon in 2017.

Johnson, who went undrafted out of South Dakota State last year, initially signed with Green Bay before joining the Chargers at the start of the season. He spent most of the fall on the practice squad but was activated for two games in November and had two carries for eight yards.

Running backs Jaret Patterson and Greg Desrosiers Jr. also turned in solid performances for the Chargers.

(Ashley Landis / Associated Press)

There’s some jostling over the backup quarterback job to Justin Herbert, featuring a replay of last summer’s competition between Trey Lance and DJ Uiagalelei.

Lance got the start and played deep into the third quarter, completing 12 of 20 passes for 164 yards with an interception. He ran for 27 yards in three carries.

Uiagalelei completed six of nine for 120 yards — 55 on that wheel route to Johnson — and had a three-yard pass to Devonte Ross for the final touchdown.

Harbaugh said both quarterbacks moved the offense well, and he was impressed with the way both dug themselves out of holes. Lance guided the Chargers to a first down after a first-and-20 start, and Uigalelei did the same facing first and 19.

“Can you move the football team?” the coach said. “Can you move the team and end up with points, field goals or touchdowns? More often than not, those drives were ending up in the end zone.

“Both quarterbacks acquitted themselves well.”

Around this time last year, the Chargers were reeling along the offensive line, having lost left tackle Rashawn Slater to a season-ending knee injury. Early in the season, they also lost bookend tackle Joe Alt. In short, the offensive line was a mess.

Now, those players are back, and it’s all about making smaller tweaks along a solid line. The question mark is at left guard, with five candidates in the mix: Kayode Awosika, Branson Taylor, Jake Slaughter, Trey Pipkins III and Trevor Penning.

Slaughter, a rookie second-round pick, started at center Thursday and moved to left guard and appeared to play well. That he can play center in addition to guard is particularly valuable, as he can provide reliable depth behind starting center Tyler Biadasz.

Harbaugh praised several offensive linemen. Asked what he liked about Slaughter in the game, he said: “Just his demeanor, his physicality, his knowing what to do.”

The play of both lines was pleasing to Harbaugh, who praised the performances of young defensive linemen TeRah Edwards and Jacobian Guillory.

Meanwhile, first-round edge rusher Akheem Mesidor wasn’t on the field much. Presumably, the coach is going to ease him into preseason games.

“He’s been impressing me all camp,” Harbaugh said. “And by design, he didn’t play a ton of snaps.”

Chargers wide receiver KeAndre Lambert-Smith had four catches in the first half Thursday but couldn’t pull in this pass against Texans cornerback Collin Wright.

(Ashley Landis / Associated Press)

KeAndre Lambert-Smith had a game-high four receptions, all coming in the first half. Harbaugh was pleased with the separation he created.

“I felt like I played fast, executed, played physical,” Lambert-Smith said. “I just did what I was supposed to do.”

He finished with 58 yards, but would have had significantly more had a pass not slipped through his hands. He had beaten rookie corner Collin Wright on a deep ball, but the pass from Lance was slightly underthrown. Wright mistimed his leap, and the ball got through to Lambert-Smith before bouncing off his hands.

“My feet got caught in the turf and it kind of messed up my whole adjustment to the ball,” the receiver said. “Wish I had that one back, honestly.”

The top three receiver spots are locked down by Ladd McConkey, Quentin Johnston and Tre’ Harris, but there’s room for one more wideout and maybe two. A rookie to watch: the speedy Brenen Thompson, who doubles as a returner.

Teams are always circumspect about doing anything too exotic during the preseason, lest they give regular-season opponents something to study. That goes double for the Chargers, seeing as all three of their preseason opponents — Houston, San Francisco and the Rams — will face them again. It’s a bit of a balancing act, though, because it’s got to be tempting to get a look at McDaniel’s offense outside the structure of a practice.

“We’re doing things we’ve been practicing,” Harbaugh said. “It’s not too different than playing a division opponent twice in a year. And don’t underestimate Mike. He’s pretty sly about setting some things up for the next time we play.”