SANTA CLARA -- The 49ers potentially face a strange, dangerous and still-largely-unfamiliar opponent Sunday afternoon:

Overconfidence.

The 49ers are the "It" team of the NFL right now. After their eye-opening victory in Green Bay last week, they have drawn plaudits from multiple precincts. Those who rank teams (and they know it's guesswork) have ranked them as either the league's best or second best. Those who overreact (and you know who you are) have the 49ers already in the Super Bowl. Those who do not overreact (including cynical sports columnists) still are impressed.

It is quite a change from, say, a year ago when the 49ers were thought of as an NFL also-ran at this point. It is only natural, therefore, to wonder if too much hubris might creep into the 49ers' mindset approaching kickoff at Candlestick.

Offensive lineman Alex Boone says no.

"I think our head coach takes care of that," Boone said the other day, citing the Jim Harbaugh factor. "The minute he feels that you're more than you are, he'll smack you down a little bit. I think that's what you need as a player -- someone who knows how a team feels mood-wise, confidence-wise, who keeps you right where you need to be."

But where are the 49ers, really, at this point? It is interesting how the NFL schedule gods have again provided the Detroit Lions to give us all a good read on that matter.

The two teams met last year in Week 6. The Lions were 5-0 and on an unexpected roll. The 49ers had a 4-1 record that included a stunning victory at Philadelphia and a frustrating home loss to Dallas. Both the 49ers and the Lions recognized that their matchup was a statement game.


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It turned out to be exactly that, though the postgame handshake ruckus between Harbaugh and Detroit coach Jim Schwartz served as a silly distraction. (But here's a tip for both men, who have been critical of the coverage: If you don't want the media to focus on the sideshow, don't create the sideshow.)

The 49ers won at Ford Field that day, 25-19, and it provided the first true sign that Harbaugh and his players were not an early season fluke but a division title contender. Alex Smith, who threw the winning touchdown pass, confirmed it was an over-the-hump moment for his team.

"It was hard-fought, coming down to the last possession," Smith said. "No question, anytime those games happen, they stick with you. Big win for us, on the road, three-hour time difference, playing indoors, hostile environment, finding a way to win in the fourth quarter. I think those are things you just build off of as the season goes on."

Now, the Lions again. They are again a good team, even if they struggled a bit in a 27-23 victory over St. Louis last week. And their coach, when he hasn't been chasing after Harbaugh, has led them to an improved record in each of the past three seasons.

So. We have yet another barometer game for the 49ers. Last year, overconfidence was never a concern for them. The roster was filled with players who were aware of the eight non-winning seasons that had preceded 2011. No way were they going to show up Sunday with a too-cool-for-school or take-it-for-granted attitude. However, after reaching the NFC title game and being anointed as the Next Big Thing by so many people, the 49ers need to prove their hunger has not abated.

Harbaugh has said he is a "big believer" in the bromide that a football team makes its biggest improvement between Week 1 and Week 2. Yet after last week's generally excellent performance in Green Bay, can that be possible?

"There are positives to use as a foundation, a platform, to get better at," Harbaugh said. "There are things you'd like to see improved."

Every Sunday is different, of course. Which is why we watch the games. The guess here is that Harbaugh has definitely mentioned the "O" word -- overconfidence -- to his employees over the past week. Boone said that when Harbaugh does his barking, it's usually in a team meeting when he senses that the players aren't dialed in properly or aren't focused.

So far, Harbaugh's barks always seem to work. But what happens if they don't?

"You've met him," Boone said. "If you continue to goof around, I don't know what the next thing would be. But I don't want to know."

Contact Mark Purdy at mpurdy@mercurynews.com or 408-920-5092.