SANTA CLARA, Calif. (AP) Mike McCarthy's Green Bay Packers circled this game among the tough challenges of the first quarter of the season, facing the familiar San Francisco 49ers in the unfamiliar confines of new Levi's Stadium for the first time.
Not to mention during a short week with a long trip out West to face a team that had Green Bay's number going into the fifth meeting in four seasons.
Aaron Rodgers and Co. were unfazed by it all, even if it took a little while to find a rhythm in a 17-3 victory against struggling Colin Kaepernick and the hapless Niners on Sunday to keep Green Bay unbeaten.
Led by a relentless, swarming defense that put Kaepernick on his back six times, the Packers started 4-0 for the first time since winning their initial 13 games in 2011.
Rodgers passed for 224 yards and a touchdown and ran 17 yards to set up a key second-half score.
''We're 4-0, we're first in the division and we're playing the kind of ball we want to play in most of the phases,'' Rodgers said matter-of-factly when asked to assess his team. ''It was a grind out there.''
Richard Rodgers caught a 9-yard touchdown pass on the game's opening drive before Aaron Rodgers got his team going in the second half after a slow start to snap a four-game losing streak to San Francisco.
The Packers certainly hope their trip to Levi's Stadium will be the first of two this season. The Super Bowl comes to the second-year, $1.3 billion Bay Area venue in four months for its 50th year celebration.
Here are five things we learned Sunday:
STUFFING THE RUN: Green Bay certainly looked better than its No. 27 ranking stopping the run, shutting down Carlos Hyde and San Francisco's second-ranked rushing offense.
Hyde was held to 20 yards on eight carries, while Reggie Bush was stuffed for no gain trying to go up the middle on third-and-11 in a play call that was immediately scrutinized.
On the ensuing drive, James Jones caught a 38-yard pass on the left sideline by barely staying in bounds. Rodgers then scrambled 17 yards to set up John Kuhn's 1-yard scoring burst.
''Our defense played lights out,'' McCarthy said. ''I think it's our best performance so far this year. Our ability to stop the run was our starting point and I thought special teams did a heck of a job.''
ENDING THE SKID: San Francisco beat Green Bay to begin and end the year in both the 2012 and '13 seasons, eliminating the Packers from the playoffs after first spoiling their season openers.
So this win might have been a little sweeter, especially with so many cheering Cheeseheads in the crowd.
Much has changed since then, including all of the departed defensive personnel for the 49ers - with Patrick Willis, Justin Smith retiring and Aldon Smith's release before he recently joined the Oakland Raiders.
''You look at that defense, they've had some guys retire over the last year, they've had some guys go other places, so it's a different opponent,'' Rodgers said.
KISS THE BICEPS: Not-so-subtle Clay Matthews made his mark on this game with a sack and some smack.
When he sacked Kaepernick for an 8-yard loss in the third quarter, the animated linebacker kissed his biceps Kaepernick-style.
FOX cameras picked him up on the mic saying, ''You ain't Russell Wilson, bro,'' in reference to Seattle's QB.
''Fortunately, we were able to wear them down both offensively and defensively and get a big road win,'' Matthews said.
KAP UNDER PRESSURE: A week after throwing a career-high four interceptions, Kaepernick was under pressure all day again, throwing another pick and taking six sacks.
He now has 14 sacks through four games after being sacked 52 times last season, second-most in the league behind Jacksonville's Blake Bortles with 55.
San Francisco (1-3) has scored just 28 points over three games while giving up 107. The quarterback was booed in the fourth quarter.
''We're an offense that can run the ball and throw the ball,'' 49ers wide receiver Torrey Smith said. ''We're not doing either well right now.''
FRUSTRATION MOUNTS: 49ers coach Jim Tomsula isn't ready for an offensive overhaul or switch to backup quarterback Blaine Gabbert, but everybody involved is feeling the heat of an ineffective scheme and a quarterback who admittedly is being cautious with his throws to avoid further mistakes.
Kaepernick, who had played some of his best games against the Packers, went 13 for 25 for 160 yards and a 55.4 passer rating.
''We've got to collectively on offense have 11 guys going in the same direction,'' coach Jim Tomsula said. ''It's not fractured. There's a little frustration there but not fractured at all.''
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This story has been corrected to show that Blake Bortles plays for Jacksonville, not Carolina.