ESPN NFL

SAN FRANCISCO -- For anybody who questioned whether new coach Jim Harbaugh could turn around the downtrodden San Francisco franchise in a hurry, his 49ers are giving every indication this year might be different.

Two weeks, two impressive wins against expected contenders.

Alex Smith threw two of his three touchdown passes to Vernon Davis, Frank Gore ran for a touchdown in his second straight 100-yard rushing game and San Francisco whipped the Tampa Bay Buccaneers 48-3 on Sunday for its best start in nine years.

"We're not putting any limitations on ourselves," Harbaugh said.

Carlos Rogers returned an interception 31 yards for a touchdown and tight ends Davis and Delanie Walker each caught TD passes of 20-plus yards in San Francisco's third straight win since blowing a late lead in a Sept. 18 overtime loss to the Cowboys.

This marked the Niners' largest margin of victory since they beat the Los Angeles Rams 48-0 on Dec. 27, 1987 -- and it matched the Bucs' worst loss ever.

"It's been a long time," Davis said of being on the better end of a rout. "To be ahead like we were today, I don't remember the last time I've seen anything like that."

But a late right leg injury to wide receiver Josh Morgan put a damper on what had been a near-perfect day.

While the Niners (4-1) beat Seattle and Cincinnati, the past two weeks are more telling: a 24-23 come-from-behind win at Philadelphia last Sunday followed by this lopsided affair against the former NFC South leader.

"He told us to stay humble and keep working," Gore said of Harbaugh's postgame message.

Josh Freeman never found the flow that made him so effective in the rout here last November and the Bucs (3-2) were a step behind in a short week after beating the Colts on Monday night.

"Flat start. Flat finish. Flat middle. Everything," coach Raheem Morris said. "We didn't even get off the plane this time."

Tampa Bay lost its cool, too -- and lost a share of the South lead in the process.

A testy Morris received an unsportsmanlike conduct penalty with 9:05 left in the third quarter for yelling in the face of line judge Mark Steinkerchner.

Just more than five minutes later, safety Sean Jones had a late hit to Kendall Hunter's head after the play was over.

Linebacker Dekoda Watson was flagged for an unsportsmanlike penalty 4 seconds into the fourth quarter that set up Davis' second TD catch.

"They were really frustrated. I felt like they gave up," Davis said. "I was telling Ronde (Barber), 'Get your guys, get your guys, y'all got to play harder.'"

With Smith making all the right calls behind center, those occasional Blue Angels flyovers for Fleet Week just added some extra entertainment on a gorgeous fall afternoon in the Bay Area.

Smith never got a chance to help during an embarrassing 21-0 shutout home loss to Tampa Bay last year. He watched from the sideline as former coach Mike Singletary chose Troy Smith to start instead.

He made his mark this time, going 11 for 19 for 170 yards and no sacks or interceptions before giving way to rookie backup Colin Kaepernick midway through the fourth.

The 49ers are 4-1 for the first time since 2002, the last time the franchise had a winning record and reached the playoffs -- four head coaches ago.

Next up is another tough test: a Week 6 road game at Detroit, with the Lions unbeaten heading into Monday night's home game with the Bears.

San Francisco came out of halftime with an 80-yard, seven-play scoring drive capped by Davis' 23-yard TD grab. Walker caught a 26-yard pass for the 49ers on their opening drive of the game.

The big plays are coming in all phases -- from Smith and Co. on offense, from special teams and from the defense.

"That's what we can do every single week," left tackle Joe Staley said.

Even the kickers did their part to secure San Francisco solid field position.

That worked out nicely for Smith, who these days is generating cheers from the Candlestick Park crowd that has let him have it with boos so many times in recent years.

One of his shining moments Sunday came when Smith had nearly gone to the ground under pressure and he released the ball at the last second to find Morgan on the left sideline for a 13-yard gain. Morgan made five catches for 75 yards before the injury.

It's those kind of situations where the old Smith would have been clobbered or sacked for a big loss. His decision-making has been spot on so far. The 49ers have only four turnovers in five games.

By halftime, Smith had hit four different receivers on completions of 12 yards or longer.

Rogers' third interception of the season, on a pass intended for Kellen Winslow early in the second quarter, stopped any momentum Tampa Bay might have gained after Gore fumbled deep in Bucs' territory.

"When you put points on the board on defense like that, it takes a lot out of an offense," Rogers said.

Rookie Chris Culliver thwarted the next Buccaneers' drive with his first career interception.

Dashon Goldson provided a nice block on Freeman as Rogers stepped into the end zone on the right side, then Goldson forced a fumble by Mike Williams late in the third that was recovered Ray McDonald.

These 49ers, alone atop the NFC West, are determined not to waste another strong start the way they did two years ago.

Smith was part of the team that began 3-1 in 2009, but wound up dropping the next four games and five of six on the way to an 8-8 finish.

Freeman went 17 for 33 for 187 yards with two interceptions and two sacks.

"It's surprising. How could it not surprise you?" Bucs center Jeff Faine said.

Game notes

Freeman's six INTs this season equal his 2010 total. ... Gore's scoring run gave him 38 rushing TDs for his career, fourth on the franchise list. ... Adam Snyder started at RG for the Niners for the second straight week.