Alex Smith and Shaun Hill were the only two competitors for the starting job through the first five days of training camp. Now, J.T. O'Sullivan has emerged as a candidate to start the season opener, Sept. 7 against the Arizona Cardinals.

"I'm open to all three right now, and that's where my mindset is," 49ers coach Mike Nolan said.

Nolan originally said he would like to decide on the team's starting quarterback by the third exhibition game, Aug. 21 against the Chicago Bears. But now he said he is willing for the competition to run its course -- no matter how long it takes.

"We're all anxious to get to one. I know I am. And, then again, I'm not," Nolan said. "It's early in camp, there's a lot of work to get done. I want to know if we do have to go to another, if we get to a second quarterback, or a third, something like that. What is he capable of doing? So, this is a valuable time for us. This is not just trying to find out who's No. 1, this is also trying to find out who gives us a chance, our very best chance, to win."

For the first time, O'Sullivan has emerged as a possibility.

O'Sullivan has endured a nomadic six NFL seasons, spending time with New Orleans, Green Bay, Chicago (twice), Minnesota, New England, Carolina and Detroit. He signed with the Lions last summer after then-offensive coordinator Mike Martz liked what he saw from watching film of him during NFL Europe. O'Sullivan won a job as the backup to Jon Kitna.

Nolan hired Martz as offensive coordinator in January. And Martz insisted that the 49ers sign O'Sullivan as a free agent. O'Sullivan and the 49ers settled on a one-year, $645,000 contract.

O'Sullivan's experience in Martz's offense gives him an edge over Smith and Hill, both of whom are trying to learn the intricacies of the system.

"There is a sense of familiarity with the offense and I'm trying to grow from that," O'Sullivan said. "What I really try to do is get better and better every day. My job is to be ready."

Said Nolan, "It's evident that he's been in it because with the limited reps he's had so far, if it was all new to him this year, he wouldn't be where he's at," Nolan said. "So he is further ahead. That is one of the reasons, too, we felt early in training camp in fairness to the other two guys, we needed to get them up to speed because J.T. does have a year under his belt."

O'Sullivan has gotten off to a strong start in training camp, based on his knowledge of the system. Nolan remains committed to giving each of the three quarterbacks a fair opportunity to win the job.

"It's early in training camp," Nolan said. "We've only been here a week. So it's still early. But that's an important decision. I don't want to sell us short. It's going to happen on the field, it's going to happen in fairness, and three guys are competing for it.

"It's not going to be 100-percent fair with reps (practice snaps), but we're doing the best we can."

CAMP CALENDAR: The 49ers have practices scheduled every day, leading up to their first exhibition game Friday, Aug. 8, at the Oakland Raiders. On Monday, Aug. 4, the 49ers will travel to Napa to hold two joint practices against the Raiders. The 49ers practice most mornings, beginning at 8:50 a.m. Every other day, they have a second full-squad practice in the afternoon. On the other days, they hold special-teams practices in the afternoon. The 49ers break camp on Aug. 22, the day after an exhibition game at the Chicago Bears.