PITTSBURGH (AP) — Justin Herbert spent two-plus quarters trying to grit his teeth through the pain of an ankle injury that doesn’t seem to be going away anytime soon.

For a while, it worked. The Los Angeles Chargers quarterback threw a first-half touchdown pass to Quentin Johnston and largely stayed out of trouble in the face of T.J. Watt and the rest of Pittsburgh’s relentless pass rush.

It all ended midway through the third quarter when Herbert dropped back to pass and Steelers linebacker Elandon Roberts crashed into him for a sack. Herbert hobbled to the sideline one play later and watched backup Taylor Heinicke muster little the rest of the way as Pittsburgh surged to a 20-10 victory.

“I did everything I could to go back in there,” Herbert said afterward, his right foot in a protective boot. “I didn’t feel like I could move around or really push off of it.”

Herbert went to the medical tent to be evaluated then spent the rest of the game on the bench as the Chargers (2-1) saw their promising start under first-year head coach Jim Harbaugh take a hit.

“Not every game is going to be a fairytale ending,” Harbaugh said.

Harbaugh declined to speculate whether Herbert will be available next week when Los Angeles hosts AFC West rival Kansas City, saying only the team will take the same “wait and see” approach it used after Herbert initially injured the ankle on Sept. 15 in Carolina.

Herbert practiced little during Los Angeles’ extended stay in Charlotte and the Chargers listed him as questionable on Friday. Herbert walked onto the Acrisure Stadium turf about two hours before kickoff on Sunday in a white T-shirt and blue shorts and spent about 30 minutes going through a typical warm-up.

Harbaugh saw enough to feel comfortable giving Herbert the nod, with the caveat he would put Heinicke into the lineup at the first sign of trouble. For two quarters, Herbert mostly stayed out of it. He made quick decisions and moved the ball with relative ease, including a 27-yard dart to a wide-open Johnston that gave Los Angeles an early lead.

Herbert could feel, however, the soreness starting to ramp up. Then he felt his ankle twist underneath him as Roberts dragged him to the ground. Harbaugh then opted to pull his franchise quarterback rather than risk further damage on a day Herbert ended 12 of 18 for 125 yards.

“I knew Justin wasn’t going to take himself out,” Harbaugh said.

So Harbaugh did, a decision Herbert didn’t try to talk his coach out of, but only after exhausting all physical options.

“I pushed myself (and) I couldn’t do it anymore,” Herbert said. “And I had a tough time walking on it, moving on it, pushing off of it. And I knew that Taylor gave us a better shot to win.”

Heinicke completed both of his pass attempts for 24 yards, but was also sacked twice on Los Angeles’ final possession on a pair of plays in which the pressure came so fast he could do little in response.

“It’s a difficult spot but I feel like my whole career has been like that, a backup, kind of be ready to go,” said Heinicke, acquired by the Chargers from Atlanta in late August. “Throughout my career, I’ve had a lot of chances to play. It wasn’t something new but playing this defense at their place on a home opener, it was tough.”

Neither quarterback got much help from a running game that did little. J.K Dobbins was held to 44 yards on 15 carries on a day the Chargers ran for just 61 yards total, way fewer than they averaged during early victories over Las Vegas and Carolina.

The Los Angeles defense also wore down late without edge rusher Joey Bosa, who left in the first quarter after aggravating the hip injury that’s been nagging him for weeks. A handful of costly penalties — three alone on Pittsburgh’s go-ahead drive in the fourth quarter — also cost the Chargers.

“(The Steelers) got the momentum at that point and kept it and held onto it,” Harbaugh said. “That’s the way it went.”

Harbaugh made it a point to praise Herbert’s toughness and that of his team. Yet he’s also well-versed in how these things go when two teams essentially on equal footing meet.

“It’s razor-sharp,” he said. “It’s credit-card (width) difference, the margin. And I thought it was right there. It was back and forth. It was right where I thought it would be and we didn’t get it done at the end there. But we’ll come fighting back.”

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