The lights at Candlestick Park were free football to win a battle of playoff teams.

The same couldn't be said for the Pittsburgh Steelers, or more specifically, Ben Roethlisberger, who battled through a high ankle sprain but committed four turnovers in a 20-3 setback.

Alex Smith connected on 18-of-31 passes for 187 yards and a touchdown, while Frank Gore ran for 65 yards and a score on 18 carries for the NFC West- champion 49ers (11-3), who stayed in contention for a first-round bye.

The Steelers (10-4) had a chance to take control of their division with a fifth straight win, but fell back into a tie with the Baltimore Ravens atop the AFC North.

Roethlisberger threw for a respectable 330 yards on 25-of-44 throws, but was picked off three times and lost a fumble.

The game was twice delayed because of power outages in the San Francisco area.