The Steelers got quarterback Ben Roethlisberger back just in time for kickoff but couldn't stop the Chargers often enough once the ball was kicked off.
A depleted defense surrendered points on the Chargers' first five possessions and then a touchdown on a 53-yard dagger late on the way to a 41-37 loss on Sunday night at SoFi Stadium in Inglewood, Calif.
The Steelers fell to 5-4-1 with their first loss since Oct. 3 (27-17 at Green Bay).
The Chargers improved to 6-4.
Quarterback Justin Herbert's 53-yard touchdown pass to wide receiver Mike Williams and kicker Dustin Hopkins' extra point finally put the Chargers ahead to stay with 2:09 remaining in the fourth quarter.
The Steelers' last gasp at another comeback was shut down on back-to-back sacks of Roethlisberger, a delay-of-game penalty and, finally, an incompletion on fourth-and-32.
Kicker Chris Boswell's 45-yard field goal with 3:24 left in the fourth gave the Steelers their first lead since 3-0 at 37-34 with 3:24 left in the fourth quarter.
The Steelers had taken over at the Chargers' 34-yard line after running back Austin Ekeler was stopped for no gain on fourth-and-1.
The Steelers made it all the way back from what had been a 17-point, fourth-quarter deficit at 27-10 and tied the game at 34-34 on a 5-yard touchdown pass from Roethlisberger to tight end Pat Freiermuth and Boswell's extra point with 4:23 left in the fourth.
That possession had begun at the Chargers' 11 after a pass that was deflected by defensive tackle Cam Heyward was intercepted by cornerback Cam Sutton.
The Chargers didn't punt until 12:52 remained in the final quarter.
It turned out to be the beginning of an eventful sequence and the precursor to a wild finish.
A second punt had to be attempted due to offsetting penalties, and this one was blocked by Steelers safety Miles Killebrew (his second blocked punt of the season)
The Steelers took over at the Chargers' 3 and eventually scored on a 1-yard dive by running back Najee Harris that followed a pass interference penalty against Chargers cornerback Tevaughn Campbell on fourth-and-goal from the 5. Boswell's extra point brought the Steelers back to within 27-20 with 11:35 left in the fourth.
The Chargers responded with a seven-play, 75-yard drive for a touchdown in 2:47.
The back-breaker for the Steelers on the march was a 36-yard scramble by Herbert on third-and-5 from the Steelers' 47. Herbert's sixth carry of the game upped his rushing total on the night to 93 yards.
Ekeler finished the drive with a 5-yard run, his fourth touchdown of the night.
Hopkins extra point pushed the Chargers' lead back to 14 at 34-20 with 8:48 left in regulation.
The Steelers countered again, this time on a 5-yard touchdown pass from Roethlisberger to tight end Eric Ebron that capped a nine-play, 75-yard drive in 3:39. Boswell's extra point made it a seven-point game again at 34-27 with 4:49 left in the fourth.
The Chargers took the kickoff to start the second half and completed a six-play, 70-yard drive for a touchdown in 3:10 that re-established a two-score lead.
It was extended on a 30-yard completion from Herbert to wide receiver Keenan Allen on third-and-13 from the Chargers' 27-yard line and finished on a 17-yard catch-and-run by Ekeler. Hopkins extra point upped the Chargers' lead to 24-10 with 11:50 left in the third quarter.
The lead ballooned to 27-10 on a 41-yard field goal by Hopkins with 3:40 left in the third.
The Steelers got back within two scores at 27-13 on a 36-yard field goal by Boswell with 14:10 left in the fourth. Their 10-play, 57-yard drive in 4:36 was highlighted by a 28-yard completion from Roethlisberger to wide receiver Chase Claypool to the Chargers' 39.
The Chargers took a seven-point lead into the locker room at halftime thanks to a 30-yard field goal by Hopkins with two seconds left before the intermission.
The scoring drive covered 63 yards on eight plays in 1:07.
The Steelers battled back from a 14-3 deficit and pulled to within four on a seven-play, 64-yard drive in 2:33 that ended on a 9-yard touchdown pass from Roethlisberger to wide receiver Diontae Johnson.
The big play on the march was a 22-yard connection from Roethlisberger to Johnson on second-and-10 from the Steelers' 48. The two also hooked up for gains of seven and nine yards prior to the touchdown.
Boswell's extra point cut the Chargers' lead to 14-10 with 1:09 left in the second quarter.
The Chargers upped their advantage to 11 on a 10-yard pass from Herbert to Ekeler that capped a 12-play, 98-yard drive in 6:54. Hopkins' extra point gave the Chargers a 14-3 lead with 3:42 left in the second.
The Chargers gained possession by stopping a pass from Roethlisberger to tight end Pat Freiermuth for no gain on fourth-and-goal from the Chargers' 2.
The Chargers grabbed their first lead of the night on a 12-play, 73-yard drive in 6:20 that ended on a 6-yard touchdown run by Ekeler. The Chargers went 3-for-3 converting third downs on the possession. Hopkins' extra point made it 7-3 in favor of the home team with 2:09 left in the first quarter.
Boswell opened the scoring with a 36-yard field goal with 8:33 left in the first.
The Steelers' game-opening drive covered 57 yards on 13 plays in 6:31.
The Steelers played without outside linebacker T.J. Watt (knee/hip), free safety Minkah Fitzpatrick (Reserve/COVID-19 list) and cornerback Joe Haden (foot) on defense.
They were without guard Kevin Dotson (Reseve/Injured list) at the outset and then lost his replacement, J.C. Hassenauer (shoulder) in the second quarter.
