Singletary said Monday that Smith will remain the team's starting quarterback this week against Tampa Bay even though Alex Smith is healthy and cleared to play for the first time since separating his left shoulder Oct. 24.
It wasn't a very difficult decision. Troy Smith has directed the 49ers to their first winning streak of the season after having one of the most prolific games by a San Francisco quarterback in the past six years.
Troy Smith passed for a career-high 356 yards Sunday to spark a 23-20 overtime victory against the St. Louis Rams, guiding the 49ers on a dramatic touchdown drive in the final minutes of regulation to keep San Francisco's postseason hopes alive.
"He's had a big part in us winning these last two games, and you want to keep that going and see how much is there," Singletary said. "Our team understands that I'm going to go with the guy that is winning right now, the guy that has the hot hand and has made the difference in the past two weeks."
But Troy Smith will have to deal with a new starting left tackle.
Joe Staley, the player tasked with protecting Troy Smith's blindside, is out four to six weeks after breaking his left leg Sunday, Singletary confirmed Monday.
The fourth-year starter was on crutches after the game.
Staley kept playing after an initial injury, but committed two penalties on San Francisco's go-ahead drive late in the fourth quarter. His holding penalty wiped out Smith's 43-yard TD pass to Vernon Davis.
Singletary said the 49ers will not place Staley on injured reserve with the hope he can return at the end of the season for a possible playoff run.
Swing lineman Adam Snyder and offensive tackle Barry Sims are the top candidates to replace Staley. Snyder started at right guard Sunday but left the game with a right shoulder injury and did not return. Snyder had a MRI exam and his shoulder was heavily bandaged in the locker room Monday, but Singletary expects him to be available to play against Tampa Bay.
Troy Smith has made a big difference since leapfrogging veteran backup David Carr to take over as the starter during San Francisco's Oct. 31 game against Denver in London. Smith had been San Francisco's No. 3 quarterback to that point and had rarely even taken any snaps with the offense in practice since joining the 49ers in September.
But he led a 24-16 comeback victory over the Broncos, then played a starring role against the Rams as the 49ers improved to 3-6 and remained two games out of first place in the weak NFC West.
Troy Smith shared his leadership philosophy in the 49ers' locker room Sunday. He has no plans to project himself any differently. He used the term "even-keeled" to describe his approach.
"As a man and collectively, you achieve things and to come in and just tell guys what the bottom line is, I don't think that is how you deal with men," Troy Smith told ESPN.com. "I think you reason with men. I think you give men the opportunity and the chance to showcase their talents and their abilities and we'll all move forward."
Troy Smith, who signed with San Francisco a week before the regular season, said he assimilated into the 49ers' locker room by showing humility.
"You need to show the guys around you that you are humble, that you are a human being, that everybody can come talk and interact and be a part of any and everything that you have going on," Troy Smith said to ESPN. "That makes it a little easier for everybody to take to you when they see you are more of a personable person."
Smith has passed for more yards in a game than any San Francisco quarterback since 2004.
Smith had at least 60 yards passing to five different receivers, the first time that has ever happened in franchise history. And he produced in the clutch, completing passes on third and 32 and fourth and 18 during a 76-yard touchdown drive that put San Francisco ahead 20-17 with 2:10 to play in regulation.
"Hopefully, the guys see that as a quarterback I'll be there for them for four quarters until we get a win," Smith said. "You want to give guys the chance to showcase their talents and abilities. We're going to attack it the same way we always do, and I'm going to continue to prepare and do the things I need to do to win."
Singletary recently said that Alex Smith would likely still be the team's starter when healthy. But Troy Smith has clearly been an upgrade over Alex, who had a 75.0 passer rating and nine interceptions while going 1-6 in his seven starts. Troy Smith hasn't committed a turnover in his two starts while throwing for 552 yards and compiling a 116.6 passer rating.
Alex Smith took his latest setback in stride. His six-year career with the 49ers has been plagued by turmoil, inconsistency and injuries since he was the No. 1 overall selection of the 2005 NFL draft.
"It's frustrating, but I wasn't surprised by it," Alex Smith said. "He's done a great job the past two weeks and we've won, so I was ready for anything. I'm going to prepare like I always have. When my number gets called, I'll be ready for this team."
Information from ESPN.com's Mike Sando and The Associated Press contributed to this report.