PER Diem: March 6, 2009

BOSTON -- It's showdown time. The two kingpins of the East, not to mention the top two teams in the Power Rankings for weeks now, meet tonight at TD Banknorth Garden when the Celtics host the Cavaliers.

I'm just back from the Cavs' shootaround, where they went unusually long -- about two hours -- as they tried to introduce Joe Smith to some of the changes they've made offensively since he left a year ago.

And presumably, they also went a little longer than usual given the importance of the game -- though they're trying hard not to overemphasize this one at the expense of others.

"If we come in here and beat these guys and lose our next six, nobody is going to remember that we beat these guys," said Cavs coach Mike Brown. "This has no more importance than when we play Miami tomorrow."

Nonetheless, it's huge. And Smith's return to the team is interesting, in a way, because it's such a barometer of how things have changed in the past year.

When we last saw Smith in wine and gold, he and the Cavs were falling just short in Game 7 in the Boston Garden a year ago -- a fact his reunited teammates quickly reminded him of today.

That team was a top-notch defensive team, just like this one, but middling at best offensively.

This year, things are different, and the new guy can tell you exactly how.

"The early offense changed up a little bit," Smith said. "As far as our main sets, everything is pretty much the same. But they switched up the early offense to get more movement, and not allow everybody to stand around and let the defense set in on our early offense."

In other words, everybody-stand-around-and-watch-LeBron is kosher for the last five seconds of the shot clock, but this time around they're not going to it as the first, middle and last options.

Cleveland has moved up to fourth in the league in offensive efficiency as a result, after finishing 19th a year ago, and that's the biggest reason the Cavs are playing the Celtics for first place in the East instead of clawing and scratching just to stay above .500.

Personnel, obviously, is a huge reason. Mo Williams' addition has added basically two shooters, since his presence also allows Delonte West to move to an off-guard role in which he has thrived.

But Brown has also made it harder for opposing defenses to lock in on King James for 24 seconds.

"Offensively, I've grown and learned, and we have as a team," Brown said. "When we flow into an offense it's different now than it was last year. There's just more movement … better spacing, more ball reversals, so we're a little harder to guard and it fits our personnel a little better."

As for Smith, he should catch on quickly. In between being asked to ponder if there was anyone in the league he hadn't played with, he joked that his well-traveled career was an advantage in rejoining the Cavs.

"We don't have too much time in practice; you just have to take it up on your own to learn the sets and learn the system," he said. "But this is something I'm familiar with and something I'm comfortable doing."

Of course, Smith also adds something at the defensive end -- an area where Cleveland has improved nearly as much as it has offensively. The Cavs recently overtook the Celtics for the top spot in defensive efficiency, and while that order may flip once Kevin Garnett returns, there can be little doubt that these are the league's two best defensive squads.

So despite the Cavs' new look offensively, D is likely to be the big story tonight. Let's get the coach's synopsis of how they stack up.

"We don't rely on steals; we don't rely on shot-blocking," Brown said. "We rely on positioning, and five guys guarding the ball. So really you can have any five guys as long as they're willing to commit to it."

"One thing we both try to do is both shrink the floor and make the paint crowded. We try not to give up paint points -- Boston's a little longer, a little more athletic than us so they might have more success at it than we do. We don't want to give up uncontested 3s; we try to make guys shoot contested pull-up jump shots or contested 3-point shots."

Interestingly, he said that the Celtics might miss Garnett's mouth at the defensive end as much as his skill -- something Brown grew to appreciate even more when he coached Garnett in last month's All-Star Game.

"[He has] length, athleticism, the ability to block shots. But more importantly, his communication is off the charts. You can tell he's one of the best in the business, especially on the back side -- shoot, the back side and the front side."

And that, ultimately, may be what swings this one in the Cavs' direction -- a win that would put them 3-up on Boston in the loss column and all but assure them home-court advantage in a potential conference finals matchup with Boston.

Which would mean a seventh game would not be played here, as it was a year ago. And for the Cavs, it would mean a much better chance of a more favorable outcome than the one the last time Smith donned a Cleveland uniform.

John Hollinger writes for ESPN Insider. To e-mail him, click here.