SANTA CLARA, Calif. — Alex Smith always considered the boos from his home crowd just part of the territory as an NFL quarterback.

He'd rather hear something than nothing at all to know they truly care.

For those numerous unfriendly jabs and the constant criticism he has endured in a roller coaster seven-year career, Smith is suddenly giving people plenty to cheer about this season for surprising San Francisco (3-1).

"You can't be sensitive," Smith said Wednesday. "I think it's tough to play quarterback in the NFL if you don't (have a thick skin). That's anywhere. You're going to face scrutiny. That's the way it is."

The 2005 No. 1 overall draft pick is thriving under new coach Jim Harbaugh's guidance and in his multilayered West Coast offense, rallying the 49ers from a 20-point third-quarter deficit to an improbable 24-23 win at Philadelphia on Sunday. Smith hopes to continue that progress through a tough home test Sunday against Tampa Bay, which is also 3-1 and whipped the Niners 21-0 last November at Candlestick Park.

Against the Eagles, Smith went 21 of 33 for 291 yards and two touchdowns without an interception. In the second-half comeback, he completed 13 of 17 for 201 yards and TDs to Joshua Morgan and Vernon Davis.

Davis, running back Frank Gore and other key members of the offense have stuck by Smith through all the ups and downs, the promotions and demotions, along the way.

"It's Alex's first time having someone who really can understand him and show him the quarterback position and put him in great situations," Gore said. "Coach Harbaugh is doing a great job with him. Alex is balling."

Smith has only two interceptions in his last 259 attempts since throwing a pick on his final pass in a 27-24 loss to the Eagles last Oct. 10. What a difference from his performance this past Sunday.

For the first time in Smith's career, he has more touchdown passes than interceptions — 55-54. He began his rookie season with 11 picks before completing his first TD pass.

At age 27, he is exhibiting the poise under pressure and heads-up decision-making Harbaugh believed Smith still had in him when the former NFL quarterback took over as the new Niners coach earlier this year.

Harbaugh quickly put his faith in Smith, handing over the playbook to the QB this spring well before he re-signed as a free agent once the lockout lifted.

"He has always struck me as a very confident guy," Harbaugh said. "Very tough guy, very mentally tough guy, very physically tough guy. He's been easy to coach, he really has. Extremely bright, book smart and football experienced. It's been easy coaching him. He's done it all."

Smith was the favorite all along to win the starting job over rookie second-round pick Colin Kaepernick. Even if he was about a week behind after getting his new deal because of the post-lockout rules for when newly signed players could practice.

For Smith, the explanation for his strides is fairly simple: just as basic as staying within himself.

"I think consciously just trying to do less, if that makes sense," he said. "I really feel like I was doing too much for a long time, pressing too hard, trying to make too many plays instead of letting it come to me. Playing within a system and letting the plays happen, really not forcing things and making good decisions. Then the big plays will come."

Smith didn't get a shot against the Bucs last time, forced to watch the embarrassing blowout from the sideline. Then-coach Mike Singletary went with Troy Smith as the starter even though Alex Smith had returned to health from a separation to his non-throwing left shoulder.

Harbaugh understands the challenges of Smith's position, the pressure to prove himself time and again to the coaches, to teammates, to an organization and its fan base — and to the skeptics. Harbaugh has said it took him years to shed the reputation of being a lousy NFL quarterback.

A college star at Michigan, he played 15 seasons in the NFL for the Bears, Colts, Ravens, Chargers and Panthers. A first-round draft pick taken 26th overall by Chicago in 1987, Harbaugh completed 2,305 of 3,918 passes for 26,288 career yards and 129 touchdowns in the NFL. He also ran for 18 TDs.

Any comparisons to his coach's playing past, Smith said, are for a later conversation. Perhaps an offseason sit-down. Still, these two have a connection.

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Smith has worked for a different offensive coordinator every year, and that clearly took its toll on him finding a consistent rhythm. Now, playing for Harbaugh, he has been steady but far from spectacular.

Yet the Niners haven't needed him to be. Harbaugh's confident, calm demeanor has rubbed off on Smith and the rest of the 49ers. Like on Sunday, when this determined bunch trailed by 17 at halftime — and later got down 20 in the third quarter — in a hostile environment only to come back and stun the "Dream Team."

"The thing that I really appreciate is, the demands or expectations, or whatever they may be, aren't crazy, aren't ridiculous. He's played this game," Smith said of Harbaugh. "He played it a long time, he's coached this game now for a long time. So, when we came in at halftime ... no signs of panic. There was nothing. It was: 'Let's get better, let's play. These are the little things we need to do.'"

Smith is doing all those little things to get San Francisco off to a strong start.