J.T. O'Sullivan will start against the Green Bay Packers on Saturday night with a chance to deliver a knockout blow in the 49ers' quarterback competition.

O'Sullivan is expected to play most of the first half in what Coach Mike Nolan on Thursday called "another opportunity to showcase what he can do." A second consecutive opening assignment gives O'Sullivan a chance to cement his status as the 49ers' No. 1 quarterback. He could essentially end the debate with two solid quarters of play.

Already, it has been an astounding rise for a player who didn't take a single team snap during the first five days of practice as he waited behind Alex Smith and Shaun Hill.

But O'Sullivan has since demonstrated the strongest grasp of Mike Martz's offensive system.

The 49ers like his quick reads and air of authority. He also offers the aggressive mentality that Martz's system favors. Asked Thursday, for example, about the fine line between being careful and cutting it loose, O'Sullivan said:

"I'm going to play quarterback exactly how they want me to play quarterback. I'm going to make the reads Coach Martz wants me to make.

"I'm going to turn the ball loose (and) on time. I'm going to trust everyone to do their job, and they're going to trust me to do my job. I don't go into it thinking I'm going to play this, sort of, tentative game."

Smith reacted to Nolan's announcement with somber acceptance. He was dealing with a more difficult issue off the field.

Smith found out Sunday about the suicide of his close friend, David Edwards, at 24.

"It's hard," Smith said. "I've talked to Coach Nolan a lot this week and I think it's a difficult situation just with what happened. I think maybe he was looking to ... I don't know. Maybe this could have been a different week, but obviously, with this going on, it kind of puts things in perspective for me a little bit.

"I'll come back and treat it the way I always have: Just focus in and take advantage of the reps I get and try to make the most out of them. It's kind of all I can do."

Edwards and Smith were as close as brothers dating to their days together at Helix High. The quarterback was excused from today's light practice to attend the services being held at the Smith home in San Diego.

Smith will return in time to face the Packers at Candlestick Park, a game that presents an awkward contrast. Smith will serve as the 49ers' second-string quarterback while Aaron Rodgers, the other passer the 49ers considered in the 2005 draft, will trot out as the unquestioned heir apparent to Brett Favre.

Asked Thursday to recall the 49ers' thinking at the time of the Smith-Rodgers choice, Nolan said: "You know, it was a long time ago, let's not go there now because it would be a lot of B.S." Rodgers will instead face off against O'Sullivan, the No. 186 overall pick in 2002.

The former UC-Davis standout has taken the scenic route to his first real crack at an NFL starting job. He has been waived four times during a career that spans eight organizations.

"From the outside looking in, if it didn't work out somewhere my attitude was I just wasn't good enough to make that team," he said. "Anything else is an excuse."

Running back Frank Gore and receiver Isaac Bruce will play sparingly, perhaps a series or two. Bruce might not play at all except that the 49ers are short-handed at receiver because of injuries.

—Tight end Vernon Davis and rookie linebacker Larry Grant exchanged punches during practice. Both players landed blows, but Grant got the worst of it. He staggered to the sideline where he was attended to for several minutes by trainer Jeff Ferguson. A team spokesman said Grant was OK.

—These injured players will not suit up against Green Bay: guard David Baas (pectoral), receiver Bryant Johnson (hamstring), running back Michael Robinson (knee), receiver Arnaz Battle (hamstring), receiver Ashley Lelie (calf) and defensive back Lewis Baker (thigh).