SAN FRANCISCO – The 49ers' offense exorcised its red-zone demons, and the defense snuffed out Ben Roethlisberger and the Steelers on Monday in a game so charged with energy that it included two power outages inside Candlestick Park.

The 49ers' gritty 20-3 win allows them to maintain their edge over the Saints for the No. 2 seed in the playoffs and, after losses in two of their past three games, bolsters confidence that they indeed are a team to reckon with in the NFC.

"It's an amazing feeling," said tight end Vernon Davis, who had six catches for 72 yards. "Most of all, we beat a great team on a national stage. That's huge. We have to give ourselves a lot of credit for that."

The 49ers' defense continued its string of dominant performances.

Roethlisberger, hobbled by an ankle injury, was sacked three times, 2 1/2 of them by rookie Aldon Smith, who now has 13 sacks on the season, a 49ers rookie record.

Roethlisberger threw for 330 yards but had three interceptions – by Carlos Rogers, Dashon Goldson and Tarell Brown – and fumbled once, setting up the 49ers' final touchdown.

After scoring only three touchdowns in their last 19 trips inside opponents' 20-yard line, the 49ers concentrated on their red-zone offense in the days leading up to Monday's game.

Early on, it seemed their endeavors were for naught.

In the first quarter, the 49ers drove the ball to the Steelers' 2-yard line thanks largely to a 12-yard third-down pass from Alex Smith to Michael Crabtree.

But Frank Gore was dropped for a loss on first-and-goal. Smith, meanwhile, missed a wide-open Kyle Williams on second down and couldn't connect with Frank Gore against the blitzing Steelers on third down. The 49ers had to settle for a 22-yard David Akers field goal and a 3-0 lead.

The 49ers got another Akers field goal later in the half after driving to the Pittsburgh 20-yard line. They went into halftime leading 6-0, but it seemed like another game in which squandered chances would hurt them in the second half.

That was not the case.

In the third quarter, the 49ers ran a rare but well-executed screen pass to Kendall Hunter that gained 27 yards and put the 49ers at the Steelers' 22. On the next play, Smith faked a handoff to the right and threw back to his left to Vernon Davis, who was pushed out at the 1-yard line.

That gave the 49ers another red-zone opportunity, and this time they wouldn't be denied.

One of the plays the 49ers practiced last week had Davis initially blocking as if the 49ers were running the ball and then darting outside in the flat. It worked to perfection.

On first-and-goal, Smith faked a handoff to tailback Anthony Dixon, pulled out of the pocket to his right and found Davis alone in the end zone for a touchdown and a 13-3 lead.

Smith, who had been sacked 18 times in the past three games, was not sacked Monday. He finished the game 18 of 31 for 187 yards and had his coach singing praises in his postgame news conference.

"He was just on the money all night long," Jim Harbaugh said. "Played great. There's no doubt in my mind that he deserves to go to the Pro Bowl. He's had that kind of season, and I think he put an exclamation point on that tonight."

A sack by Aldon Smith and a fumble by Roethlisberger on the ensuing Steelers drive gave the 49ers another trip to the red zone in the fourth quarter.

This time, they drove to the Pittsburgh 5-yard line before giving Gore the ball on a delayed handoff. Gore bounced to his left and crashed into the end zone for the team's final score.

Said Davis: "It all worked out exactly like we planned it."

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