SAN FRANCISCO — The Seattle Seahawks came into Candlestick Park and proved that the NFC West will be no cakewalk in 2012, taking swings at the defending division champions from the very start of the game.

The 49ers hit right back, clamping down on the Seattle offense in the second half and trudging off the field with a 13-6 victory Thursday night.

"That was the most physical 30 minutes of football in that second half that I've ever seen our team play," San Francisco coach Jim Harbaugh said afterward, unable to hide his elation.

Down 6-3 at halftime, the Niners put the ball in Frank Gore's hands, and dared the Seahawks to do the same with Marshawn Lynch. Seattle's workhorse back ran for 55 yards in the first half, to 39 by Gore. But the 49ers controlled both sides of the line of scrimmage after halftime. Gore finished with 131 yards, averaging 8.2 a carry, to Lynch's 103.

And presented with two final chances to drive the field and tie the score late in the game, the Seahawks went nowhere behind their rookie quarterback, Russell Wilson. In fact, they actually lost yards on their final drive. Their last gasp ended when Wilson's pass to Ben Obomanu on fourth-and-17 came up a yard short of a first down.

The 49ers could have accepted a safety on the play, as guard Paul McQuistan was guilty of a chop block in the end zone. But Harbaugh, far from his days of running up the score against opposing coach Pete Carroll, declined the penalty so his quarterback, Alex Smith, could take a knee and run out the clock.

Gore looked invigorated in the second half, but at times it looked almost easy behind an offensive line that was killing the Seahawks' interior defense. Center Jonathan Goodwin and trapping guards Alex Boone and Mike Iupati opened huge holes for Gore and his understudy, Kendall Hunter.

"I think we just got angry," Boone said. "We just went out there said, &‘Hey, we want to be a physical front five. This is a great defense, this is a great week to prove it.' We did a good job of coming back in here (to the locker room), regrouping, really kind of refocusing on what we needed to do best. And I thought it was a great second half."

It was the San Francisco defense that really rose to the occasion — as it could not do four days earlier against the defending NFL-champion Giants. New York bullied the 49ers in the fourth quarter of that game. Seattle didn't have the horses, or the will, to do it.

For a long while, it looked like this game would end with scores divisible by 3, but the 49ers finally reached the promised land on their first drive of the second half. Handing off to Gore and mixing in short passes, Smith led his team on an impressive 86-yard drive, finishing with a 12-yard touchdown pass to Delanie Walker — aided by a block from fellow tight end Vernon Davis.

Smith was 5 of 5 for 60 yards on that drive, just 9 of 18 for 80 yards the rest of the game. He threw an interception in the end zone to kill another promising opportunity early in the fourth quarter, shortly after safety Dashon Goldson has set up the 49ers with his own pick against Wilson.

The first half was a grinding game of field position, and more often than not, the 49ers had the upper hand. But it was Seattle that moved the ball more efficiently. Lynch ran hard, often fighting for extra yards after contact. And Wilson looked more capable than Smith before halftime. He finished was 6 of 13 at the break, but finished 9 of 23 for 122 yards. His receivers dropped at least four of his passes.

The Seahawks wound up with field-goal attempts after each of their first three possessions. Steven Hauschka booted a 52-yarder, then added a 35-yarder before missing from 50 yards. David Akers hit a 38-yard field goal for San Francisco just before the first quarter ended.

"That football team is a good football team," Goldson said. "They kind of remind us of us. They're young, hard football team, plays fast. And got a lot of good players."

After those first three Seattle possessions, Carroll's team went punt, end of half, punt, interception, punt, punt, turnover on downs.

The 49ers waited six weeks for their first divisional game. They proved that even though the gap seems to have been narrowed, they're still the best in the West.

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