The 49ers lead the NFL in turnovers - with O'Sullivan personally responsible for 17 of them - and sacks allowed. But O'Sullivan made up for some of those negative plays with a penchant for picking up big chunks of yardage down the field. O'Sullivan completed 30 passes of 20 yards or more in the first 71/2 games.

In one of interim head coach Mike Singletary's first moves, he benched O'Sullivan and promoted backup Shaun Hill to the starting role. Hill will make his third career start when the team returns to action Monday night against the Arizona Cardinals.

"Shaun is a natural leader," Singletary said. "He leads in a different way. I just think, obviously, with him in there right now, he feels good. There's an energy about it. Going forward, I'm just excited to see what he does with the opportunity."

The 49ers offense is almost certain to show a different look against the Cardinals, as Hill might not thrive in an offense that utilizes a bunch of seven-step drops.

If Hill has showed anything in his 12 quarters of NFL action, it's an ability to be accurate in the short-passing game. He appears to be a ball-control kind of quarterback.

In fact, in Hill's first two drives after taking over for O'Sullivan the 49ers had their two longest possessions of the season. The 49ers' first drive under Hill lasted a season-long 7 minutes, 22 seconds. The second drive lasted a season-high 15 plays. The 49ers scored 10 points on those two drives.

"I think rather than favoring the shorter routes, the intermediate routes, I just think he really tries to find and take what the defense has given him rather than trying to force it," Singletary said. "His decision-making process I think right now is good."

Hill, in his seventh NFL season, played in the first three games of his NFL career last season after injuries to Alex Smith and Trent Dilfer. Hill completed 54 of 79 passes for 501 yards with five touchdowns and one interception.

When Hill entered Oct. 26 against the Seattle Seahawks in place of O'Sullivan, he completed 15 of 23 passes for 173 yards and a touchdown.

But Hill said the 49ers will not have to change their offensive philosophy with him at quarterback.

"No, I don't think so," Hill said. "It's the same offense, the mentality is going to be the same. No, I don't think that the mindset changes."

Hill signed a three-year, $6 million contract extension that included a $1.95 million signing bonus. The 49ers signed him to the new deal and declared he would compete against Alex Smith for the starting job.

Hill and Smith began training camp in competition for the starting job. However, after a week of camp, Martz decided his best quarterback was O'Sullivan, who entered in the team's No. 3 role.

Hill was the first to be removed from the starting competition. But Hill used his time in the background wisely in order to learn Martz's offense.

"I feel like I'm a lot further along than I was in training camp in the offense," Hill said. "I've been able to sit back and watch J.T. in the offense, to kind of see some of those things in action that coach Martz was talking about in training camp.

"These eight weeks I've continued to learn the offense and I feel far more advanced in it now than I was back in August."

SERIES HISTORY: 35th regular-season meeting. The 49ers lead the series 19-15. The Cardinals won the previous meeting, 23-13, this season. They have won five of the past seven games against the 49ers.