CHICAGO — J.T. O'Sullivan made a perfect case to start. And Alex Smith's counter-argument didn't measure up.

O'Sullivan threw for 126 yards and a touchdown in his limited time while Smith struggled, and the San Francisco 49ers beat the Chicago Bears 37-30 on Thursday night.

Although the third preseason game usually is a dress rehearsal for the opener, coach Mike Nolan would not select O'Sullivan as the starter this week. This game might convince him.

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 should be enough to beat Smith, who came on early in the second quarter and was 6-for-17 with 83 yards and a touchdown.

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.

Shaun 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.

RAMS' JACKSON SIGNS 6-YEAR, $44 MILLION DEAL: Steven Jackson signed a six-year, $44 million contract, ended a 27-day holdout, and was on the field for practice with the St. Louis Rams on Thursday.

And all was forgiven.

Coach Scott Linehan, who conducted a month of practices without the centerpiece of the offense, joked that he gave Jackson "a big hug" and then asked for a loan. Offensive tackle Orlando Pace, no stranger to holdouts, said he was happy "big time, big time" to see the bruising runner. Defensive tackle La'Roi Glover said simply, "Things are pretty good at Rams Park right now."

The 235-pound running back had been entering the final season of a five-year, $7 million deal he signed as a first-round pick in 2004. Linehan said he understood the business end of the game after Jackson got a deal that includes more than $20 million in bonuses and puts him third on the salary scale on the team, trailing only quarterback Marc Bulger and Pace and fifth among NFL running backs.

"It was great to see him," Linehan said. "There's no up side to being adversarial in these kind of deals. You've just got to stay positive and you've got to focus on who's here, and have trust and faith in the people that are working on getting everything done."

Jackson, 25, said both sides compromised during negotiations that stayed underground and generally cordial. Gregarious by nature, he kept silent publicly while getting frequent text-message updates from teammates and Linehan, and then flew from his home in Las Vegas to St. Louis on Wednesday when the deal was imminent.

After doing individual drills and a bit of team work in his opening practice, he said he hoped to retire as a Ram. He also pledged to be ready for full duty in the Sept. 7 opener at Philadelphia.

"No one gets 100 percent of what they would like to happen, but me and my agent are happy," Jackson said. "Of course, there were heated debates on the phone but no one attacked publicly. I still feel the same way about this organization as I did last year the last game of the season."

It won't be all roses. Jackson expects a rude welcome from Rams fans after he criticized them last year for a lack of commitment. The Rams failed to sell out three games and the Edward Jones Dome had a healthy dose of Packers and Steelers fans for late-season games.

"You definitely expect mixed reviews," Jackson said. "When you're talking about this kind of money a lot of people can't really understand why would you turn your back on a contract? Business is business."

It'll be at least a week before he gets his first preseason carry. Linehan said Jackson would be in uniform Saturday night against the Ravens but would not play while he conditions his body for football.

The team plans to get Jackson plenty of extra work and will even use the warm-up time before the preseason game to help him get up to speed. Jackson spent 20 minutes on a treadmill after practice, catching up on his cardio work.

"Really, you can't simulate the game," Linehan said. "It's more the conditioning factor of starting and stopping, and getting in the huddle and doing all that. We have plans to do some extra things with him, even when we're not practicing."

Jackson, coming off his third consecutive 1,000-yard season despite missing four games with injuries, justified his holdout while still under contract because of the lack of guaranteed money in the NFL. He based his decision to stay away instead of reporting to camp and continuing talks on the risks of playing his position.

The Rams cut off negotiations on the first day of training camp until Jackson showed up, after the running back turned down a deal the team said would have put him in the upper echelon of running backs.

"Taking a lot of hits, you never know if you can jeopardize it," he said. "The only safe bet to not signing a new deal right away is staying out of harm's way."

Backing up that point, Jackson missed four games with a groin injury and part of a fifth with a bulging disc last season. The Rams lost all five games while going 3-13.

Former teammate Marshall Faulk criticized Jackson's durability and second-guessed whether he deserved a big contract in a recent radio interview.

Jackson declined an opportunity to fire back.

"All things are forgiven," he said. "Some people don't agree and some people do agree and that's just what it boils down to during a holdout. Before I made the decision to hold out I took that into consideration."

The Rams had made signing Jackson to an extension an offseason priority and approached Jackson's agent not after the season, but negotiations stalled when Jackson switched representatives and signed with Eugene Parker in late June. Jackson said the death of owner Georgia Frontiere last January also held up talks.

Jackson has averaged 115.7 yards from scrimmage since his rookie year, fourth best in the NFL. He led the NFL with 2,334 yards rushing and receiving in 2006 and his 90 receptions in 2006 is sixth-best by a running back in league history.

TEXANS' FULLBACK ACCUSED OF MARIJUANA POSSESSION: Houston Texans fullback Jameel Cook was arrested and charged with marijuana possession Wednesday.

A Fort Bend County sheriff's deputy stopped Cook at about 7:30 p.m. because his 2007 Mercedes sedan had no front license plate or registration sticker, sheriff's department spokeswoman Terriann Carlson said Thursday.

He's free on a $500 bond after authorities said he had about two grams of marijuana, no valid Texas driver's license and no proof of liability insurance.

The 29-year-old Cook was charged with a misdemeanor after the deputy searched the car and found a plastic bag containing two grams of marijuana, Carlson said.

The team would not comment.

Cook, who lives in Missouri City, joined the Texans in 2006 and played in all of the team's games last season. He previously had played for the Tampa Bay Buccaneers, who drafted him in 2001.