San Francisco 49ers rookie quarterback Trey Lance's second preseason game went a lot like his first one -- in reverse.

Lance got off to a quick start in last week's game against the Kansas City Chiefs, hitting an 80-yard touchdown pass to wide receiver Trent Sherfield on his second pass attempt before completing just one of his final seven attempts. But on Sunday night against the Los Angeles Chargers at SoFi Stadium, it took Lance longer to find a rhythm.

After his first three series, Lance's passer rating was 0.0, as he went 1-of-5 for 9 yards with an interception thrown too hard and a bit too high for wideout Mohamed Sanu. Lance also took a sack, as those drives ended with a punt, a pick and another punt.

Lance shouldered the blame for throwing too high and hard for Sanu and fellow wide receiver Deebo Samuel on the drive before the interception, but Lance said those mistakes helped him settle in.

"I was frustrated, for sure, but at the same time, I learned so much from each of those drives that it was easy to just turn the page," Lance said. "I think I was just as confident from that point on as I went throughout the game."

From there, Lance got it rolling, sparked by another deep connection to Sherfield, this time for 41 yards. Lance completed seven of his next eight attempts for 93 yards and two touchdowns on his final three series before calling it a night.

The 49ers went on to win 15-10.

"I understand whatever Trey does, the eyes are going to be on him," 49ers coach Kyle Shanahan said. "I don't want him to have that pressure, but that's also the reality of this business. ... I thought he came out much more locked in, more comfortable. I thought we had a chance to start pretty fast and we didn't. Then it started to kind of stack up a little bit where it seemed like it was going the wrong direction. That's why I was pumped about getting that two-minute drill at the end ... I was real happy with how he finished."

Lance, whose first drive came behind the starting offensive line (without left tackle Trent Williams and center Alex Mack), settled in on his fourth series, taking over with 57 seconds left in the first half at San Francisco's 25 and hitting Sanu for a 5-yard touchdown with 12 seconds remaining. He fired a strike to wideout Travis Benjamin for a 16-yard score in the third quarter on his sixth and final drive.

Lance finished 8-of-14 for 102 yards and two touchdowns with an interception for a passer rating of 89.9. He was sacked twice out of his 30 snaps, before giving way to third-string quarterback Nate Sudfeld.

"I think, for me, especially in the situation I'm in, learning as much as I can and being able to go back and watch the tape tonight and tomorrow with the coaching staff and the quarterbacks in the room, I think that's where I grow and where I win the most," Lance said.

The Niners' initial quarterback plan was for Jimmy Garoppolo to play a series, have Lance play two series and then reinsert Garoppolo back in the game.

But Garoppolo's first drive was long enough that Shanahan opted to end Garoppolo's night after his third-down pass in Chargers territory sailed a bit high and off the hands of wide receiver Brandon Aiyuk for an interception corralled by Chargers cornerback Asante Samuel Jr.

Garoppolo finished 3-of-6 for 15 yards with the interception for a passer rating of 16.7.

Through two preseason games and most of training camp, the 49ers' quarterback situation has remained mostly status quo, but Lance worked with the starting offense for a full, eight-play series in joint practice with the Chargers on Friday and then got a series with the first-team unit Sunday night.

Asked after the game if he has seen anything that would change how he views the initial plan of Garoppolo as the starter and Lance as the backup, Shanahan demurred.

"No, I haven't seen that," Shanahan said. "I would love for it to be more and more each week, but I think the situation is pretty similar right now."

Moments later, however, Shanahan also declined the opportunity to name Garoppolo his Week 1 starter, noting he will probably wait until closer to the Sept. 12 opener at the Detroit Lions.

"No, I'm not making that announcement," Shanahan said. "Not tonight."