SAN FRANCISCO — The Battle of the Backups, as it turned out, was no battle at all. While the Chicago Bears' Jason Campbell folded under a barrage of sacks and hard hits, the 49ers' Colin Kaepernick established himself as a potential star.

The Niners delivered a 32-7 victory at Candlestick Park on Monday night, dismissing one of their primary playoff competitors as easily as Kaepernick eluded pass rushers.

Making his first NFL start, the second-year quarterback completed 16 of 23 passes for 243 yards, a pair of touchdowns and a passer rating of 133.1, doing most of the damage in the first half when this game was somewhat in question.

"We all know the talent that he has, and what he's capable of," wide receiver Kyle Williams said. "But him coming out there and just balling like that, making every throw, it's tough to say you expected him to come in and make every single throw like he did. It seemed as if he couldn't miss."

Kaepernick has enjoyed some nice moments as a spot fill-in for Alex Smith this season, but most of his appearances have had the whiff of novelty, with Kaepernick running as frequently as he threw. With Smith sidelined due to a concussion he suffered against the Rams last week, Kaepernick ignored the gimmickry and played like a classic QB. He threw from the pocket when he was able, passed on the run when he had to and distributed the ball to seven receivers.

The Bears more or less dared the 49ers to throw, stacking the box with eight or nine men to start the game. So Kaepernick threw, frequently after run-fakes, and it looked easy from the start.

As a point of reference, Joe Montana completed 5 of 12 passes for 36 yards in his first NFL start, for a passer rating of 49.3. Steve Young hit 16 of 27 for 167 yards (a rating of 77.2) in his debut with the Tampa Bay Buccaneers. Jeff Garcia was best of the three in his NFL premier, with 21 completions in 33 attempts for 243 yards and a pair of touchdowns; his rating was 106.0.

Kaepernick outdid all of those successful 49ers quarterbacks, leaving fans to ponder the long-term future of their offense — and the short-term as well, with Kaepernick potentially challenging Smith as the starter.

"I think right now we're in a situation where we have two great quarterbacks," left tackle Joe Staley said. "We won tonight with Kaepernick and we've won a lot of games with Alex. And Alex has played great football for us."

Indeed, Smith completed 25 of 27 passes in his previous two outings, before suffering a head injury on a fourth-and-1 sneak against the Rams.

Kaepernick made a lot of people forget those numbers with a stunning first half. The 49ers (7-2-1) scored on their first four possessions — a field goal, a touchdown, a touchdown and another field goal — to open a 20-0 lead over the Bears (7-3). Kaepernick hit tight end Vernon Davis for 22 yards to set up one of David Akers' kicks, floated a gorgeous throw to streaking Kyle Williams for 57 yards to get in position for a 3-yard touchdown pass to Davis off of play-action, and set up Kendall Hunter's 14-yard scoring run with another picture-perfect pass, again to Davis for 32 yards.

After that one, Davis came to the sideline and bowed dramatically to his young thrower.

"I was just so proud of him at that moment because the ball that he threw me, it was one of those balls that you see Tom Brady throw," Davis said. "Second window, right on the money."

Kaepernick began the second half with another drive and finished it with a 10-yard touchdown pass to Michael Crabtree, drifting to his left before waiting for Crabtree to slip open.

It was revealed after the game that Smith had shared the repetitions at quarterback Wednesday and Thursday. But when the effects of his concussion lingered later in the week, coach Jim Harbaugh and offensive coordinator Greg Roman started giving most of the snaps to Kaepernick. The coaches told players Sunday night that Smith would be ruled out, and the team made it official Monday morning.

Kaepernick's first-half tally: 12 of 15 for 184 yards and two touchdowns, with a passer rating of 140.0. The 49ers' yardage advantage over the hapless Bears at that point was 249-35. After 30 minutes of play, it was all but over.

The Niners were just as impressive on the defensive side of the ball. Chicago lost Jay Cutler, its No. 1 quarterback, to a concussion, too, and Campbell, the former Raiders starter, could not rally his team.

Aldon Smith set a Monday night record with 5? sacks, leading a defensive effort that sacked Campbell six times, intercepted him twice and forced him to fumble twice more, and held the Bears to 3.0 yards per rushing attempt.

"Coming in, there was a question about who was the better defense, or just questioning us in general," Aldon Smith said afterward.

And now?

"I think we showed tonight who it was," Smith said.

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