SAN FRANCISCO – It wasn't the welcome-to-the-NFL moment Eddie Lacy was hoping for, but he has already moved on from it.

On the fifth carry of his pro career on Sunday, Lacy fumbled, and the 49ers recovered at the Green Bay 14-yard line, setting up a touchdown that proved pivotal in San Francisco's 34-28 victory over the Packers at Candlestick Park.

The fumble occurred early in the second quarter and sent Lacy to the bench, replaced for two series by James Starks and then by John Kuhn in the two-minute drive at the end of the half. To Lacy's credit, when he was reinserted into the game in the second half, he bounced back and produced, but it was a tough lesson to learn with the Packers' hopes for an improved running game thrust upon him from the get-go.

"Fighting for extra yards," Lacy said of the play, which led to the ball getting "a little loose." "I should have gone down and protected the ball a little more, but I tried to get extra yardage, and it was a mistake on my part."

The Packers likely would have gotten off the field allowing only a field goal after the turnover had the officials not allegedly assessed penalties incorrectly. On third down after the fumble, 49ers QB Colin Kaepernick ran out of bounds short of the first down, but personal fouls on Green Bay's Clay Matthews and San Francisco's Joe Staley were ruled offsetting, and the down was replayed. As dead ball fouls, the penalties should have reportedly canceled one another out and it should have been fourth down, but with the third-down redo, Anquan Boldin caught a 10-yard TD pass.

In any event, when sent to the bench, Lacy had just four yards on five carries, though he also had a 31-yard gain on a screen pass to set up Green Bay's first TD. He came back in the second half to post nine rushes for 37 yards, including a 2-yard TD dive over the pile that gave the Packers a brief 28-24 lead in the fourth quarter.

On the TD drive, Lacy had runs of six, seven, five and six yards before the scoring plunge. He said he wasn't trying to make up for the fumble necessarily, just trying to forget about it.

"You have to put plays like that behind you, because if you keep it in mind, then most likely it will happen again because you're thinking about it and you don't want it to happen again," he said. "So I just put it behind me, came out and just kept playing."

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Not great, not bad:** Rookie left tackle David Bakhtiari wasn't overwhelmed by 49ers pass rusher Aldon Smith by any means, but he was charged with allowing 1 ½ sacks in his NFL debut against one of the league's premier sack men.

In Bakhtiari's defense, it appeared the sack he allowed on the second snap of the game was an offensive miscommunication of some kind. Bakhtiari went low immediately at the snap, trying to cut Smith down to the ground, an indication the play is a quick hitter with the ball coming out of the quarterback's hand right away.

But Aaron Rodgers didn't have anybody to throw to, and Smith shook off the cut-block attempt and got to Rodgers easily.

"If the ball didn't get out, I should still get him to the ground," Bakhtiari said.

The other sack came early in the fourth quarter and was shared by Smith and Ray McDonald. Bakhtiari was simply beaten off the edge on that one.

Still, those were the only two sacks of Rodgers, who dropped back to pass 40 times, and far more experienced linemen have had worse days against rushers like Smith. But Bakhtiari was far from satisfied.

"I don't want to be good as a rookie, I want to be good as a left tackle," Bakhtiari said. "I'm not mad, but I'm not ecstatic about how I played."

Kickoff duty: Punter Tim Masthay handled kickoff duties for the Packers instead of kicker Mason Crosby, and he acquitted himself well.

His first two kickoffs were returned 30 yards apiece by the 49ers, with Masthay making the tackle on the first one and saving possibly a touchdown. He missed the tackle on the next one, though, with Davon House needing to clean that one up.

Masthay then added three touchbacks in the second half, with the last two going well beyond the back of the end zone. Masthay also had a strong day punting, averaging a 44.8-yard net on six punts.

Aside from Masthay, the Packers didn't help themselves much on special teams, though. Twice in the second quarter, penalties in the return game backed the Packers up and forced them to start drives from their 4- and 13-yard lines. Then in the fourth quarter, just after the 49ers regained the lead at 31-28 with under six minutes left, returner Jeremy Ross made an ill-advised decision to bring a kickoff out of the end zone from four yards deep, and he only got to the Green Bay 9-yard line.

The Packers went three-and-out and didn't get the ball back again until only 26 seconds remained in the game.

Stops and starts: The Packers were never able to score on consecutive drives on Sunday, and two turnovers in the first half certainly didn't help. But neither did five three-and-outs, including two in the fourth quarter with the game in the balance.

"Three-and-outs, we have to get rid of those," receiver Randall Cobb said. "We have to keep our defense off the field, give them some rest and some time to recover."

Cobb joined Jordy Nelson in going over 100 yards receiving in the game. Both caught seven passes, with Nelson gaining 130 yards and Cobb 108. For comparison's sake, the offense scored 28 points against San Francisco this time versus just 24 in the playoff game (the defense got one TD then in the 45-31 defeat), and the Packers held a fourth-quarter lead, something that was never within reach back in January.

But all that was absolutely zero consolation to the players in the locker room, who have now lost to San Francisco three times in one calendar year.

"If you don't win the game, you don't win anything," Cobb said. "There's no such thing as a moral win."

Injury update: The only injury the Packers reported from the game was a stinger to outside linebacker Nick Perry, who left the field late in the fourth quarter.

Additional coverage - Sept. 8

• Instant Replay: 49ers 34, Packers 28
• Editorial: Kaepernick's legs weren't the problem
• Locker Room Report: Boldin made big plays for 49ers when it counted
• Game Recap: Packers' heart finds more hurt in San Francisco
• Postgame Press Conferences
• Game Highlights: Packers at 49ers
• Locker Room Interviews
• Game Photos: Packers at 49ers