WALTHAM — James Posey stole the ball.

Where was Johnny Most when we needed him?

Larry Bird and John Havlicek had made similar thefts near the end of humongous playoff games, forever etched in Boston Celtics' lore.

Posey's moment came with the Celtics leading Game 6 of the Eastern Conference finals, 83-79.

With 1:49 remaining, Rajon Rondo had a chance to put the Detroit Pistons away with a 19-foot jumper. But he missed.

Posey dove for the loose ball, tapping it back toward the basket, where Tayshaun Prince caught the ball.

Apparently, Posey's tip wasn't the stuff of legends.

"James was trying to save the ball and he tipped it back toward the basket," said Celtics coach Doc Rivers. "That was not a smart play."

What happened next was. Posey got up off the floor and began running back to the defensive end.

"As I ran down the floor, I noticed Tayshaun was looking for help and looked the other way (with his back to me)," said Posey said of his steal with 1:40 to play. "I just got lucky and tapped the ball away."

Two Paul Pierce free throws later, the Pistons were cooked.

"I, unfortunately, didn't see the steal," said Rivers. "I was yelling at everyone to get back on the defensive end. The next thing I know, James has the ball. ... That's James Posey."

We hardly know Posey. He isn't a member of the Big Three and he doesn't say much.

But Posey is a true Celtic.

"He epitomizes what a Boston Celtics player is," said Rivers. "He is unselfish. And he only cares about winning. I love those kinds of players."

The first Celtic off the bench, Posey is sixth in scoring for the Celtics this postseason at 6.1 per game.

Besides hitting one or two big 3-pointers when nobody is guarding him, his chief contribution is defense.

The versatile 6-foot-7 forward is the guy who gives a break to Pierce, Rondo, Ray Allen or even Kevin Garnett.

The former Xavier All-American often covers the best player on the floor, even if it's just for a few minutes. It started with Atlanta's Joe Johnson, Cleveland's LeBron James, Detroit's Chauncey Billups and Richard Hamilton and now reigning MVP Kobe Bryant.

"I can't tell you what our game plan is right now," said a smiling Posey. "I will cover who they tell me to cover."

Of course, Posey won't be on a island covering the Lakers superstar. The Celtics defense is predicated on help and even Posey, one of the top defenders in the league, will need help with this one.

But the fact that Posey can slow (or wear) down a top scorer for few minutes while Pierce gets a breather might be the difference between winning and losing.

"I can't tell you what it means to have someone like James," said Ray Allen. "He just plays hard. He's got those long arms. He's got quick feet. And he's strong."

Posey also is a winner. He was a starter on the Miami Heat team that won a title two years ago. It was an experience that had the Celtics vying for his services immediately after last season ended.

But Posey was playing hardball, wanting more money, which the Celtics didn't have. About three months passed and he still didn't have a home.

"Eddie House called. Then Doc called. Then other coaches called," said Posey. "It was a tough summer for me. And just hearing so many of them wanting me, well, I finally said yes."

The Celtics got him on the cheap, about $3.2 million, for one year, with a similar deal for next year at his option. It was half of what he had been making in Miami.

But he swallowed his pride and realized within a week it was a discount worth taking.

"All of the guys were already here, working out together, KG, Paul, Ray ... everybody," said Posey. "They didn't have to be here but everybody was. It really struck me. This was going to be serious."

Serious is all the 31-year-old Posey knows.

"You think of all the great sixth men the Celtics have had," said Rivers. "James fits in with all of them. The guy cares so much about winning."

As for his coffin-nailing steal to close out the Pistons series on Friday night, Posey smiles.

"I got a text message from a friend telling me about 'Posey steals ball,' " he said. "I think it's funny. You think of all great players that have played here. I hear about 'Havlicek stole the ball.' It's cool."

Posey stayed late after practice yesterday, shooting about 50 3-pointers. He made about half of them.

"I'd love to get excited but it's not time yet," he said. "As Shaq told me after we won the (Eastern Conference finals) two years ago. We haven't done anything yet. I remembered that. We're here to win it all. That's the goal. That's why I'm here."

John Havlicek couldn't have said it any better.

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Celtics' super sixth men

PLAYER%COMMENT

Frank Ramsey%Pioneered the role under Red Auerbach

John Havlicek%Ran opponents into the ground

Paul Silas%Smart, owned the boards

Kevin McHale%Scoring machine, defensive stopper

Bill Walton%Key to 1986 championship team