Every serious playoff team needs an intimidating closer, and the 49ers have their guy in dominant form.

Large fellow. Inspires his teammates. Weighs almost 300 pounds. Takes the game over when the drama builds and the stadium shakes.

Defensive lineman Justin Smith = Mariano Rivera?

Well, he has been this season, for this team, and possibly in more ways than just the obvious one.

On a team that continues to rise to the NFL summit, Smith is the foundation, the quiet standard-bearer and undeniable tone-setter.

You know what else he is? Smith is the 49ers’ nonchalant superstar, a Mariano with shoulder pads, cool reactions and bad intentions.

“He should be in the MVP category,” coach Jim Harbaugh said of Smith. “He’s got a huge heart — just a big, strong, mighty man.”

On Sunday, with the 49ers desperately holding onto a 27-20 lead in the final minutes, it was Smith who slapped away Eli Manning’s fourth-down pass deep in 49ers’ territory to close out the game.

The 49ers win (to get to 8-1). Save Smith (2).

On Oct. 2, with the 49ers feverishly holding onto a similar lead, in a similar late-game situation, it was Smith who chased down Eagles receiver Jeremy Maclin, knocking the ball loose for a 49ers recovery.

The 49ers won that one (3-1). Save Smith (1).

What’s going on here?

“I guess it’s better to be lucky than good,” Smith said Sunday, while his teammates loudly saluted him nearby.

That, of course, is a dry understatement but totally typical of Smith’s shoulder-shrugging approach.

His teammates know better, and swear by him. Even the best of them.

“I told him on the sidelines, series after series, how much I respect him,” Patrick Willis said of Smith. “I think he’ll be one of the best players I’ll have ever played with in my life.”

But you also get that part of Smith’s leadership comes from his absolute refusal to talk about himself, if he can at all help it.

Leadership and team chemistry are often exaggerated traits when talent, strength and strategy are what usually win games.

But when you look at this 49ers team, and hear how they speak about each other, you realize that these players feel uniquely responsible to each other.

“It’s a focused, unshakable team,” Smith said. “And I think that’s going to do well for us going forward.”

It’s not just Justin Smith, of course. The 49ers are getting immense performances out of Alex Smith, Frank Gore, Willis, Vernon Davis, David Akers, Joe Staley, Mike Iupati, Carlos Rogers and many others.

But the truest representative of the total team mentality is Justin Smith; you sense that Harbaugh is speaking of him when Harbaugh praises the entire team.

“I don’t take any credit for it,” Harbaugh said Sunday, speaking as effusively as he has all season. “This is these guys. These men. These mighty strong men. They’re easy to coach. They’re a joy to be around.

“They come to work, they’re about each other, more than anything. They’ll diminish themselves to raise up a teammate. That’s who they are.”

In a locker room suddenly full of stars, Smith is a different kind of energy source.

In fact, when I told him that Harbaugh said he should be in the MVP discussion, Smith shook his head violently.

“I think Carlos (Rogers) gets my nod,” Smith said.

And when I asked Rogers about Smith, Rogers hit the same note of self-effacement.

“That was the play of the game right there,” Rogers said of Smith’s bat-down. “If they would’ve scored on that drive, my two picks didn’t mean anything.

“That’s our closer. That’s our big-time player. People talk about him getting old, he isn’t doing this or that. But Justin’s making plays.”

Smith is the guy who doesn’t say much publicly, who never comes out of the game when the 49ers defense is on the field, who is the leading edge of the defense, and who just happens to make the biggest plays in the most anxious moments.

Sunday, Smith actually chipped in two successive close-out plays.

On the third-down play right before the bat-down, Smith lunged across the line of scrimmage to hold back Giants running back D.J. Ware on a surprising run call.

Nobody in the locker room said they definitely knew Smith had something special up his sleeve, but nobody said they were at all surprised that he did.

He’s the closer. He’s the guy they look to, and lean on, and have built upon.

As the games get bigger and bigger, the 49ers know that Justin Smith won’t shrink. He’ll just keep leading the way, quietly.

Read Tim Kawakami’s Talking Points blog at blogs.mercurynews.com/kawakami. Contact him at tkawakami@mercurynews.com or 408-920-5442.