The San Francisco 49ers will start Alex Smith at quarterback ahead of Shaun Hill this week, while fellow signal callers Jake Delhomme, Kerry Collins and JaMarcus Russell are all sweating on their job prospects.

49ers coach Mike Singletary brought Smith on for Hill at half time during Sunday's defeat in Houston, and he immediately brought about a big change in their fortunes.

After just 50 yards in the first half, San Francisco made 247 in the second, 206 via Smith's arm, and also scored three touchdowns as a powerful comeback came up just short.

Singletary had seen enough of 2005 number one draft pick Smith to play him from the start this weekend against Indianapolis.

"As far as this upcoming week, in terms of quarterback, Alex Smith will be the quarterback," said Singletary.

"As far as 'Will Shaun Hill be back?' and all this other stuff - we're not going to be a flavour of the month kind of team.

"I wanted to make the decision based on who gives us the best chance to win."

Two veterans hanging onto their jobs by a thread are Tennessee's Kerry Collins and Carolina's Jake Delhomme, both of whom have had dreadful starts to the season.

Panthers man Delhomme faces being benched for the first time in seven years after starting this season the way he ended the last - as a real turnover machine.

Delhomme committed six turnovers in the Panthers' play-off defeat against Arizona last season, and he already has 13 interceptions in six games this year for the 2-4 Panthers - who have the worst turnover ratio in the league.

Coach John Fox is trying to stand by the man who surprisingly led the team to the Super Bowl in 2003 and who signed a new big-money deal during the off-season, but it is getting harder to justify as his slump goes on.

"I still believe Jake is our best quarterback. I have no reason to believe otherwise, truth be told," Fox said.

"But collectively we'll do whatever it takes for us to improve. What that is, I can't honestly tell you at this second."

Delhomme benefits from having no real quality behind him as a back-up, but fans in Tennessee may soon see their former first-round draft pick back under centre if Kerry Collins does not shape up.

15-year veteran Collins also signed a new two-year deal after leading the Titans to an NFL-best 13-3 record last season, but they languish on 0-6 after a winless start this time around.

2006 first-round pick Vince Young is waiting in the wings after overcoming some personal problems, and although head coach Jeff Fisher is publicly backing Collins he may be ready for a change.

"We've had a week to do some different things," Fisher said. "Especially considering the circumstances with the record, there are things that you need to do differently. Let's just say I am not going to be as specific and open-ended from a competitive standpoint."

JaMarcus Russell is another overall first pick not living up to his reputation as he struggles to find his own team-mates in Oakland.

Russell had given the ball away three times during the Raiders' 38-0 mauling by the New York Jets when head coach Tom Cable benched him in favour of Bruce Gradkowski.

Russell has the second-worst passer rating in the NFL this season and thrown just two touchdowns and looks to be on borrowed time if his performances do not improve.