Considering they got beat 34-0 in the first game ever played in their new $1.3 billion stadium, today’s film session couldn’t have been a butterflies-bobbing-in-a-meadow sort of picture for the 49ers.

That said, preseason is largely about individual performances, especially among the young guys trying to claw their way onto the 53-man roster, and a few players did stand out for the right reasons. Top of that list may have been cornerback Kenneth Acker, the sixth-round draft pick from SMU.

Acker had just one official tackle and one pass defensed Sunday, but his impact was greater. The pass breakup was on a potential touchdown throw from Denver quarterback Zac Dysert to Greg Wilson late in the third quarter. And Acker was involved in two of the more memorable plays that occurred during “mop-up time.” They came on consecutive snaps.

On first-and-goal from the 49ers’ 1-yard line with 53 seconds left in the third quarter, Dysert lobbed a timing pass to Bennie Fowler, who leaped and caught the ball in the end zone against Acker. The apparent touchdown was waved off, though, when Fowler was called for offensive pass interference.

“At first I didn’t see the call,” Acker told me after the game. “But I felt him two-hand push me and I was looking at the ref that was immediately in front of me, and I was like, ‘OK, you’re not gonna do anything.’ And he kind of hesitated. That’s why I looked around, and then finally the ref behind me, I saw the yellow flag come in.”

Even though he was outmuscled for the ball, the confident Acker saw the play as a personal victory.

“I felt like if he didn’t push off, I maybe would’ve had a pick on that play,” he said. “Because I had good position, and it was like the only separation he got was from that push.”

The next play, Dysert tried to hit Fowler across the middle and Acker intercepted at the 2-yard line. He had a nice return, too – 26 yards – and celebrated accordingly. Then he found out that 49ers linebacker Aaron Lynch, a fellow rookie, was offside on the play.

“It definitely was disappointing, just because I finally got my hands on the ball, and then it got called back,” Acker said. “I think the real disappointment came from not knowing the penalty was called at first. So I was kind of hyped, and I got kind of excited and then had to walk back to the sideline and catch my breath, and then, ‘Hey, Ack, you’re still out there.’ So that was really the point where I had to snap back in and put myself back into the game.”

Two big moments, neither of them an official play from scrimmage. Still, Acker came away convinced that he had made a good impression on the 49ers.

“I feel like this week I really came into my own,” he said. “Coming in at first, it was like trying to understand everything. I mean, I feel like every rookie that’s not one of those main guys just goes through that time where it’s like, ‘Dang, am I really here? Am I gonna be able to stay?’ ”

Acker increased his chance of staying. In fact, he might be making it tough for the Niners to decide whether to try to stash him on the practice squad when they cut down to 53 players. At the same time, Acker knows he hasn’t done enough yet to seal his position.

“I’m just gonna try to keep going uphill, because you can’t just have one good game and feel like you made it,” he said. “I got a pick but it got called back. Nobody cares about the preseason pick that got called back. So it’s like I just gotta keep proving myself every day, so we’ll see how it goes.”