SAN FRANCISCO — Mike Singletary’s band of brothers is in trouble, and it knows it’s in trouble.

Sunday, you could see Singletary and the 49ers players start to sweat. You could feel the nerves jangling.
You could sense a nervous hush creeping over the entire franchise.
After the 49ers’ dispiriting 34-27 home loss to Tennessee — their fourth consecutive loss — you could hear some of the passion evaporate from their words.
Why wouldn’t it? They have believed. And it is not, as of yet, coming true.
“We’re still going to stay positive,” linebacker Patrick Willis said. “Nobody’s going to point the finger at any side of the ball, not at the special teams, not at the coaches. We’re just going to continue to work, continue to fight as a team. We’ve still got a lot of football left. It’s not over until our last game.”
The other losses could be explained: edged at Minnesota, Indianapolis and Houston, run over by a hot Atlanta team at Candlestick.
But losing to Tennessee amid a series of crippling 49ers errors, and falling to 3-5, is a development that cannot be shrugged off.
It’s not trivia. It’s not a building block. It might not even be the beginning of the end of the 2009 season.
This could be the middle of the end.
“In my mind, as long as we continue to fight, as long as we continue to play the way we played today, we’ve got a chance — if we take away the stupid stuff where we’re killing ourselves,” Singletary said.
There is no sign that the mistakes will stop, however. Gamblers say that you always bet the streak, and right now the 49ers’ streak is mistake, lose, lose, mistake, lose, lose.
Important point: This is nothing close to the chaos of previous administrations.
The players aren’t quitting or splitting into rival factions. They still are totally Singletary’s players, and this remains a tightly bound team.
In fact, Willis spent five minutes huddled with Alex Smith in the locker room after the game to make sure Smith knew the defense still supported him.
But they’re losing, including Sunday to a team that started the season 0-6. They’re making errors. They’re in flux. They’re under pressure. They’re antsy.
They switched quarterbacks two weeks ago, with great hope for Smith. But he went back into Old Alex Mode on Sunday “” one fumble, three interceptions.
Their defense is supposed to be good enough to hold up on such occasions, but it got whacked around for 135 yards by Titans running back Chris Johnson.
That’s why Singletary and the players still spoke bravely after the defeat, but not as surely.
“I still think we have enough games left to get into the playoffs,” nose tackle Aubrayo Franklin said. “But we’ve got to go out there and play better than we did today.”
It’s not over. They’ve got a half-season left, starting Thursday night against the Chicago Bears. A quick winning streak puts them right back into playoff contention.
But the 49ers haven’t won a game since beating St. Louis on Oct. 4. And that is a long time.
Singletary probably didn’t want to be an example of anxiety, but he provided it anyway, with a series of fitful answers to normal postgame questions.
“I don’t care about the Cardinals,” Singletary said when asked about falling two games behind in the NFC West. “I care nothing about the Cardinals. I care nothing about anything else that’s happening in the NFL. I don’t care about that.”
Sunday, after much public debate and urging, the 49ers made an effort to open up their offense “” using two-tight-end, shotgun sets “” to some success.
But it also helped expose the passing game, which led to the four crucial turnovers.
“You’re asking me why did we do it?” Singletary snapped after he was asked about the pass-first game plan. “You’re asking me all week why wouldn’t I do it. Now you’re asking me why did I do it.”
Just a little sensitive. The nerves are tingling.
Nothing wrong with the reaction. It’s natural.
Singletary’s an absolutist: He has rebuilt the spirit of this team by declaring that victories will be inevitable if the 49ers just do the right things. Period.
Will happen.
And yet the victories are not coming. What do you tell your players when they do almost everything you ask, except win?
There is no answer for that. There never has been.