Even so, 49ers coach Mike Nolan wasn't ready to announce a starting quarterback.
Although the third preseason game usually is a dress rehearsal for the opener, Nolan wouldn't declare a winner in the quarterback race.
"We will talk about it more (Friday)," Nolan said. "I would like to watch the film, talk to our players, before any announcement or anything like that is made. But I did like what I saw in all three of them."
After two mediocre outings against Oakland and Green Bay, O'Sullivan couldn't have performed any better against the Bears.
He was 7-for-8 with a perfect 158.3 passer rating in his third preseason start. He led the 49ers (2-1 preseason) to field goals on the first two possessions and a two-play, 77-yard touchdown drive on the third one. He hit Vernon Davis with a 40-yard pass and then scrambled to his right before throwing a 37-yard touchdown pass to Jason Hill to give the Niners a 13-10 lead less than a minute into the second quarter.
"That was a great play call," he said. "Jason did a great job of running so fast across the field and just made a great play on the ball."
And O'Sullivan did a good job, too. The question is whether he did enough to beat Smith, who came on early in the second quarter and was 6-for-17 with 83 yards and a touchdown, even though Nolan wasn't about to make an announcement. He even left the door open for Shaun Hill, who played well late in the game.
He entered the game after Chicago's Garrett Wolfe fumbled the kickoff following Hill's touchdown pass, giving the Niners possession on the Bears' 16. Moran Norris ran it in from the 1 to make it 20-10.
Smith also led the Niners on a 62-yard drive that ended with a 12-yard touchdown pass to Dominique Zeigler, giving the 49ers a 27-20 lead with 9:28 left in the third quarter. Otherwise, it was a rough night for him.
Hill replaced him late in the third quarter and was 6-for-7 with 60 yards against the Bears' reserves. But after Thursday's game, the starting job appears to be O'Sullivan's even though there was no announcement.
"Everybody wants to know who the starting quarterback will be," Davis said. "I don't know. I have no idea. Everybody looks good to me."
He was 10-for-17 with 147 yards, two touchdowns and no interceptions for Chicago (0-3). He had four passes of 18 yards or more, including a 55-yarder to Mark Bradley -- a big improvement over the first two preseason games, when his longest completion was 17 yards.
"I thought I played well and I thought we played well as a unit," said Orton, who started 15 games as a rookie in 2005 and three last season. "I thought as a unit we had been playing all right, we just hadn't been scoring points. Finally we kind of got over that and put up 20 points in the first half, which was good."
Smith said Orton didn't need a good showing to keep his job.
"He's our quarterback, and I think he can play good football for us, but it was good to see him validate that tonight," Smith said.
Orton and Grossman had split time with the first team in practices and the first two preseason games, with neither gaining a big statistical advantage. Even so, Smith went with Orton. And Grossman did nothing to prove him wrong, going 1-for-4 with 6 yards.
He entered the game with 9:21 left in the third quarter and got booed less than a minute later, nothing unusual there. A frequent target at Soldier Field, he heard the boos when Keith Lewis broke up a pass to Marty Booker.
Bears running back Kevin Jones carried 3 times for 30 yards in his first preseason appearance. He started by breaking off a 34-yard run on the first play from scrimmage of the third quarter, not a bad entrance for a guy who got derailed by season-ending injuries to his foot and knee the past two years with Detroit.
Chicago's Danieal Manning delivered two big kickoff returns - a 60-yarder and 75-yarder in the first quarter - to set up a 21-yard touchdown catch by Davis and a 21-yard field goal by Robbie Gould that made it 10-6.
- The Bears held a moment of silence for NFL Players Association executive director Gene Upshaw, who died of pancreatic cancer on Wednesday.
- The Bears held TE Desmond Clark out of the game with a sprained knee. They were also without DE Mark Anderson (thumb surgery), LB Nick Roach (concussion), long snapper Patrick Mannelly (stinger) and LT Chris Williams (back surgery).
- San Francisco was without WR Bryant Johnson (hamstring), LG Adam Snyder (right ankle), RT Jonas Jennings (broken hand), WR Arnaz Battle (hamstring) and RB DeShaun Foster (death in the family).