SAN FRANCISCO — Fooled by the preposterously warm weather at Candlestick Park on Sunday night, the 49ers won an August preseason game. Or so it seemed.

The Niners grabbed a lead just a minute and a half into the game, methodically built a 21-point halftime advantage, then more or less played out the string against a team, the Houston Texans, that really had no chance of mounting a serious challenge. The lack of drama made it feel as though the starters had retreated to the sideline and the second stringers were left to finish things off — a sensation heightened by guys like Tony Jerod-Eddie, Dan Skuta and Michael Wilhoite playing prominent roles on defense.

The final tally: a 34-3 victory for the 49ers, and they barely worked up a sweat in getting there.

Quarterback Colin Kaepernick's statistics through three quarters — before he teamed up with tight end Vernon Davis on a deep touchdown pass — included four completions in 13 attempts, for 45 yards. Those numbers were appropriate in 1972, but are almost unrecognizable in today's NFL. And yet the 49ers led 21-0 at halftime, tied for their largest first-half lead under Jim Harbaugh.

"Anytime you can get up on 'em — like you said, it was efficient," right guard Alex Boone said.

Powering the effort for the 49ers was their pass defense, which came up with three interceptions. It's debatable how much of that had to do with tight coverage, and how much lay on the shoulders of Matt Schaub, Houston's embattled quarterback.

Schaub was already one of the most despised men in Texas coming into the game, thanks in part to his perplexing late-game interception that opened the door for a loss to Seattle last week. Sunday's game did nothing to improve his standing. He threw three interceptions — two to cornerback Tramaine Brock, who was playing in place of injured Nnamdi Asomugha in the nickel — and one to 301-pound defensive tackle Jerod-Eddie, and Schaub probably should have thrown a fourth; rookie safety Eric Reid dropped a pass that was right in his mitts.

Texans coach Gary Kubiak pulled Schaub in favor of T.J. Yates with 14:16 to play, though Kubiak said afterward that Schaub remains his starter.

The evening started precisely as Texans fans feared it would, with Schaub throwing a pick-6. On the third snap of the game, on third and 6, he tried to hit receiver Andre Johnson on a short out, and Brock left his man to step in front of Johnson for the interception. Eighteen yards later, the Niners had a 7-0 lead.

"Huge play," Harbaugh said. "Great to see Tramaine — he's such a great guy, such a great worker, such a great team guy. He was in perfect position to play the coverage, and then finished the play."

It was the fourth game in a row that Schaub had an interception returned for a touchdown, an NFL record he'd rather ignore.

Half of the first quarter elapsed before the 49ers touched the ball, but their offense quickly went to work on a 65-yard scoring drive. Kaepernick was crisp, completing several passes to set up Frank Gore's short touchdown run, which gave San Francisco a 14-0 edge.

Brock got Schaub again in the second quarter. He didn't find the end zone this time, but he did give the 49ers a short field. Runs by Kaepernick and Gore set up Anthony Dixon, who bounced to the outside and scored for a 21-0 lead.

It was a breakout game for Brock, who entered the game with two interceptions in 32 career games. In the postgame locker room, he submitted to a rare crush of media.

The icing on the 49ers' cake came in the fourth quarter when Kaepernick hit tight end Vernon Davis in stride on a corner route, and he outran future Hall of Fame safety Ed Reed en route to a 64-yard touchdown.

Kaepernick finished with just 113 passing yards. This one was won on the ground, with the 49ers grinding out 177 yards of rushing, including 81 on 17 carries by Frank Gore. That performance, combined with last week's against St. Louis, has San Francisco fans believing their team has returned to the power game that made it so formidable in Harbaugh's first two seasons here.

All in all, it was a great day for the 49ers, who watched the division-rival Seahawks fall to Indianapolis earlier in the day. After a wobbly start, San Francisco is 3-2 and playing good football again.

"It's tough. Look at the schedule: Green Bay, Seattle, the Colts, St. Louis, Houston. That's a tough schedule, but we're up for it," Gore said. "We're the 49ers. When we're on, we can do what we want to do."

Sunday, the 49ers were on from the outset.

<i>You can reach Staff Writer Phil Barber at 521-5263 or phil.barber@pressdemocrat.com.</i>