The 49ers can improve to 4-1 on Sunday and relive memories of their 2002 season, when they last pulled off that start and parlayed it into a playoff berth.
The 49ers can lose and spark fears of a 2009 relapse, when a 3-1 record was followed by four consecutive defeats to crush then-coach Mike Singletary's honeymoon period.
So which will it be? Can the 49ers hold serve at home and beat a fellow NFC upstart, the Tampa Bay Buccaneers (3-1)? Or is humility coming?
A third consecutive, non-division victory would make the first-place 49ers runaway favorites in the lackluster NFC West. Positive thinking like that abounds after a 10-day road trip featuring comeback wins at Cincinnati and Philadelphia.
The 2009 stumble from 3-1, however, serves as a humble reminder to these 49ers, who insist much has changed in two years.
"It feels, yeah, very different, for me, just from the team perspective," quarterback Alex Smith said.
"That was different, though," running back Frank Gore added.
"It's a lot different," tight end Vernon Davis said.
The most obvious change is their coaching. Jim Harbaugh and a revamped staff have installed a detailed, blue-collar approach that is succeeding at the season's quarter mark.
"The coaching staff believes in us and gives us a chance to make plays," tight end Delanie Walker said. "They're dirty, and we're dirty."
The 49ers haven't evolved into an offensive
Last week's second-half comeback at Philadelphia, however, delivered a flood of confidence after the 24-23 win.
"The performance we put on last week, I've never been a part of something like that," Davis said. "When I saw that, I said this team can take it all the way."
Added Walker: "Just the confidence level, I can see it."
Two years ago, the 49ers fell to 3-2 when they lost 45-10 to the Atlanta Falcons at Candlestick Park. Shaun Hill, not Smith, served as the 49ers' quarterback and was previously unbeaten in seven home starts. Gore, meanwhile, sat out with an ankle injury.
Two years later, Smith is flourishing for an efficiency standpoint and the uncontested starter. Although Gore again is battling a sore ankle, he overcame it last Sunday to score the deciding touchdown at Philadelphia.
That victory marked the 49ers biggest comeback since their 2001 team's wild-card playoff win over the New York Giants, when they rallied from a 24-point deficit for a 39-38 triumph.
"Now we know that we can be a great team," Gore said in comparing this season to 2009. "We've got more talent, and our coaching staff (does) a great job of drawing it up and explaining to us, like as long as we don't give up, we can do it."
They didn't give up when the Eagles took a 23-3 lead in the third quarter. Aside from unexpected offensive brilliance, the 49ers defense stiffened. Justin Smith sealed the victory by forcing a fumble that Dashon Goldson recovered with just over two minutes remaining.
"The defense is playing sha-bam," Walker said. "You can't run on them, and they're getting turnovers when they need to."
The 49ers' plus-eight turnover differential is matched only by the undefeated Detroit Lions, who host the 49ers next Sunday.
As for the Buccaneers, they are 3-1 for the fourth time in five years. They didn't make it to 4-1 last year but did finish 10-6, including a 21-0 win at San Francisco on Nov. 21. Although Troy Smith served as the 49ers' quarterback in that shutout, Alex Smith hasn't forgotten the defeat.
Nor is Alex Smith basking too much in this season's success.
"If you start feeling really good about yourself, it would be crazy," Smith said. "It's still very early. We have to get better, absolutely."
Harbaugh endorsed that message.
"I prefer that we be simple in that we have humility," Harbaugh said. "We might not have known when we gained (humility), but speaking for myself, speaking for my team, we know we've gained it. That carries with a note of loss and true pride.
"Overconfident, over-prideful -- those things can lead to big trouble."
Or, as the 49ers' 2002 season showed, a 3-1 start can lead to a cherished playoff berth.