Los Angeles: A pair of stadium power outages could not prevent the San Francisco 49ers from overcoming the Pittsburgh Steelers 20-3 Monday in a gritty matchup between playoff-bound teams.

The lights went out at Candlestick Park on two occasions, delaying the game's start for 20 minutes before again halting the action for about 15 minutes early in the second quarter.

The blackouts, however, had little effect on the home side, who controlled the game from start to finish.

"It was unusual, you don't expect to deal with something like that - let alone twice," 49ers quarterback Alex Smith said.

"It was a big game with two 10-win teams. This game was about respect."

San Francisco forced Steelers quarterback Ben Roethlisberger, playing through an ankle sprain, into two first-quarter interceptions to limit Pittsburgh's air attack and take a 6-0 halftime lead.

The 49ers squeezed the life out of the Steelers in the second half. Smith tossed a one-yard pass to Vernon Davis for a 13-3 third quarter lead before Frank Gore capped a drive with a five-yard touchdown run with 9:10 left in the contest.

San Francisco finished with just 287 total yards but dictated the action to keep pace for a top NFC playoff seed.

"I think we need to acknowledge that was 49ers football. We played the game on their terms," said Pittsburgh coach Mike Tomlin.

"We didn't do enough. We had an opportunity and didn't seize it."

Having already clinched the NFC West Division, the 49ers (11-3) are tied with New Orleans for second in the conference, two games behind leaders Green Bay with two games to play.

Roethlisberger finished with 330 passing yards but three interceptions for the Steelers (10-4) who had their four-game win streak snapped and missed the chance to take the outright lead in the AFC North. Pittsburgh are tied for first with Baltimore.