SAN FRANCISCO -- Chris Johnson got to perform his celebratory dance after all.

Six plays after his 81-yard touchdown run was overturned, Johnson took a pitch from Vince Young and scurried 2 yards for a go-ahead score and led the Tennessee Titans to their second straight win with a 34-27 victory over the stumbling San Francisco 49ers on Sunday.

Young showed his comeback is legitimate, outplaying fellow first-round draft pick Alex Smith down the stretch. Young has been clutch twice in as many weeks, getting the Titans (2-6) in the end zone when it mattered.

Johnson converted on fourth-and-inches for his second TD of the day, making up for those six points that were negated only a few minutes earlier after it was determined he stepped out of bounds on the long run. Going for it when the Titans could have tied it with a field goal was a sign of coach Jeff Fisher's faith in Young and Co. to get it done.

The Titans beat Jacksonville last Sunday to end an eight-game losing streak dating to December. Suddenly, this team has found some much-needed momentum. Tennessee has its first back-to-back wins since victories over the Lions and Browns in Weeks 13 and 14 last season on the way to a 13-3 finish.

Smith threw two interceptions in the final 6:24 and three in all, fumbled twice and was sacked four times -- not the kind of day he'd hoped for in his first home start in more than two years.

Smith took over the starting job at halftime against Houston on Oct. 25 when coach Mike Singletary benched Shaun Hill.

After Johnson's score, Chris Hope intercepted a pass by Smith on San Francisco's ensuing series to set up a 28-yard field goal by Rob Bironas, then Cortland Finnegan added a late 39-yard interception return for a touchdown to seal it.

Stunned San Francisco (3-5) has lost four straight following a 3-1 start -- and the 49ers have little time to recover. The Chicago Bears come to town for a Thursday night game.

Young and Johnson were all smiles on the sideline as they stood together and waited out the end of this one.

After Johnson's TD was reversed, Young hit Justin Gage on a leaping catch between two defenders for a 33-yard gain to put Tennessee in the red zone. The Titans kept converting the big plays.

Johnson finished with 135 yards on 25 carries -- 53 of those after his TD run was called back. Young, who got his starting job back last week, was 12 of 19 for 172 yards and ran for a 7-yard touchdown. Johnson has 959 yards rushing through eight games.

Vernon Davis had career highs of 10 catches and 102 yards for San Francisco in a game pitting two rebuilding quarterbacks who have resurrected their careers with improved play of late. But this was a big step back for Smith, the No. 1 overall pick in 2005 who was booed in the waning moments by those fans who stuck around for the finish.

Jason Hill caught touchdown passes of 12 and 3 yards for the 49ers, who had better turn things around in a hurry if they want to make the playoffs and end a franchise-worst streak of six straight losing seasons.

Frank Gore was held to 83 yards on 15 carries with a 3-yard TD run but made several key plays in the second half. He also had seven catches for 75 yards.

Young made a pretty 49-yard completion to Gage in the first quarter for the Titans, who settled for a 21-yard field goal by Bironas. Gage had four receptions for 97 yards.