The Tennessee Titans may be a different team with Vince Young re-installed as the starting quarterback and Chris Johnson coming off the best game of his career.

San Francisco's Alex Smith can relate to Young as far as being a high draft pick trying to resurrect his career after a difficult start.

Young and Johnson look to help the Titans earn a second straight victory when they try to hand the banged-up 49ers a fourth straight loss Sunday.

Tennessee earned its first win last week, beating Jacksonville 30-13. Young, named the starter after Kerry Collins guided the Titans to an 0-6 mark, responded by completing 15 of 18 passes for 125 yards and a touchdown.

It was Young's second start since 2007.

"He looked all right out there," owner Bud Adams said about the No. 3 overall pick in the 2006 draft. "I think he's coming around a lot. I think there's some things that happened to him early in his career that didn't let him concentrate on football. I think he realized he needed to work at it hard. And he has shown that."

While Young was steady, the Titans' first victory was really keyed by Johnson. The second-year running back rushed for a franchise-record 228 yards on 24 carries and scored two touchdowns.

Johnson leads the league in rushing with 824 yards after entering last week fifth. His five runs of over 40 yards also lead the NFL.

"It feels real good to look at some of the guys who have played before me, then come in and break a record," Johnson said. "But records are made to be broken."

Young improved to 19-11 as a starter, and he's 6-2 against NFC clubs. In contrast, Smith is 11-20 after he lost his first start since 2007 last week, 18-14 at Indianapolis.

Smith - the top overall pick in 2005 - played well in relief of Shaun Hill on Oct. 25 in a 24-21 loss at Houston, throwing three touchdowns to tight end Vernon Davis to rally the 49ers (3-4) from a 21-point deficit.

He completed 19 of 32 passes for 198 yards against the Colts with one touchdown to Davis and one interception, falling to 3-6 in starts against AFC teams.

"I thought Alex did very well," coach Mike Singletary told the 49ers' official Web site. "I was very pleased to see him make some throws. I was very excited and anticipated this game for him because I knew the rush was going to be coming at him."

Singletary received bad news Monday when he learned that cornerback Nate Clements and left tackle Joe Staley will be out for this game.

Clements, who has missed only one game in his career, has a broken right shoulder blade and is out for up to eight weeks. The 49ers signed cornerback Keith Smith on Tuesday.

Staley has a sprained right knee and will miss a game for the first time in his three-year career. Barry Sims is expected to take his place in the lineup.

"Obviously we're going to miss Joe Staley," Singletary said. "In terms of how it's going to affect our offensive line, which in essence is how it's going to affect our offense, you find a way to win. You find a way to work around it.

"Obviously he will be missed. We think a lot of Joe Staley. I'm hoping he's back real quick because he helps us tremendously. At the same time I know our offense will continue to get better."

Singletary has said he will go with the best players who give the team a chance to win even if it means he has to regularly shake up the lineup.

"This team right now is going through some changes," Singletary said. "You're seeing guys step up, young guys stepping up, and some other guys stepping back. It's going to continue to be that way. I believe in the best 11 guys on the field. Whoever that is, that's who's going to be out there."

San Francisco appears to be fairly healthy up front on defense, and that will be important as it tries to contain Johnson. The 49ers have the league's second-ranked rush defense, allowing 84.9 yards per game.

The Titans won 33-22 at home in the last meeting Nov. 27, 2005.