Justin Herbert made his second straight appearance in the preseason on Thursday night.
But the Chargers quarterback only saw the field for a trio plays as the unit went three-and-out to open the game.
The Bolts began with an Omarion Hampton run to the right that lost a yard before Herbert found tight end Charlie Kolar in the flat for a 9-yard gain.
But Herbert’s third-down pass intended for Ladd McConkey fell incomplete as the offense trotted off the field.
“The three plays they were in there … kind of hard to judge them on three plays,” Harbaugh said.
Harbaugh noted that the plan was for the starters to play one series, meaning he didn’t consider putting them back out there for another drive.
“We had a plan … stuck to it,” Harbaugh said.
The Chargers rolled out a starting offensive line of, from left to right, Trey Pipkins III, Kayode Awosika, Jake Slaughter, Cole Strange and Joe Alt.
Like Herbert, Alt exited the game after three plays as he was replaced by Travis Burke at right tackle.
Slaughter got the start at center after Tyler Biadasz sustained a left knee injury during Tuesday’s joint practice with the 49ers.
3. Defensive starters get early work
The majority of the Chargers defensive starters also saw action Thursday night, getting a dozen plays in against the 49ers top offense.
The unit — which didn’t include Derwin James and Khalil Mack — saw plenty of third-down work.
The Bolts starters faced three different third downs on San Francisco’s opening offensive drive and allowed the 49ers to convert each time.
But safety Elijah Molden finally put an end to the sequence when he notched a pass breakup on third down to force a punt near midfield.
All in all, the Chargers top defense gave up 39 yards on 12 plays before giving way for younger players to get meaningful reps.
The plan for the third and final preseason game is for the Chargers starters to play two series instead of one.