So who's the pressure on now?

This NBA playoff series between the Cavaliers and Boston Celtics has bounced back and forth between two cities, with each team winning twice on its home court.

That's what is supposed to happen.

But the dynamics of the Eastern Conference semifinals change from city to city and from game to game.

Safe to say that when the Cavs came back from Boston, they knew that they were in a must-win situation. Fall behind 3-0 or 3-1, and the series would tilt decidedly toward the Celtics.

Now the Celtics return home after losing twice in Cleveland, and looking bad doing so.

The first loss was one-sided, and in the second, the Celtics did not show up in the fourth quarter.

Unless you count a 12-point fourth quarter ''showing up.''

And unless you count being on the receiving end of an in-your-face,

windmill dunk for the decade ''showing up.''

That dunk symbolized the fourth quarter.

LeBron James broke free for the first time for a highlight-film moment, and the Celtics were unable to stop him. In fact, their efforts to stop him looked meek. Much like their fourth quarter.

Through the series, there has been one constant: The Cavs have played excellent defense. The Celtics are shooting 40.5 percent. They are scoring 81.5 points per game. They are 15-for-58 from 3-point range.

And the alleged Big Three have turned into a Very Good One who didn't come through in the fourth quarter of Game 4.

Ray Allen is 12-for-36, which means he's making one in three shots. Rajon Rondo has taken more shots than Allen; Sam Cassell, five fewer. Which kind of states how involved Allen has been in the Celtics' offense.

Paul Pierce is 18-for-52, and it seems that every time that James does something, Pierce thinks he has to try to do something better. It's not working.

Kevin Garnett has been very good, shooting 32-for-57 and leading the Celtics in rebounding. But he inexplicably sat the first four-plus minutes of the fourth quarter in Game 4 and missed his only two shots.

This is not the stuff from which legends are built. Or banners hung.

James, meanwhile, continues to struggle with his shot. But he compensates in so many other ways.

Monday, he had 13 assists, four in the fourth quarter, when he took control, assisting or scoring on six of the Cavs' last seven baskets.

And he ended the game with his dunk from the rafters — right over Garnett.

The Cavs had the edge at home. The Celtics had the edge at home. How things go in Game 5 will not depend on what happened in Game 4.

But there certainly can be a carryover.

Especially from that dunk, which had the crowd at Quicken Loans Arena pushing the outside of the building with noise. It might even get James going full tilt offensively.

''It takes his game to another level,'' the Cavs' Daniel Gibson said. ''Once he gets a major dunk or a big-time 3-pointer and he gets rolling, I don't think there's anybody or any team that can stop him from doing what he wants to do.''

The scene after the dunk was something.

While the Q celebrated, the Celtics tried to sit down and talk strategy. As they did, the folks at the Q played the dunk over and over and over again on the screens hanging over center court. Each time the ball went in, the crowd roared. One can only imagine the feeling that it produced from the Celtics if they happened to glance up at the scoreboard.

It had to be one of two things — unnerving or maddening.

Last year, James had a dunk over Rasheed Wallace of the Detroit Pistons that affected the tone of a series the Cavs went on to win.

How it affects the Celtics, if it does at all, will be answered in Game 5.

It's hard to say a team has the momentum in a series when both teams have won twice at home, but if anyone has carryover heading to New England, it would seem to be the Cavs.

That being said, they surely will face a difficult environment in Boston. Much has been made of the Celtics not winning on the road in the playoffs, but they have yet to lose at home. Also, the Celtics' threesome might have struggled in Cleveland, but these players have been All-Stars for a reason.

Gibson said the Cavs left Boston after Game 2 knowing things had to change if they were to win in Cleveland.

The Cavs did that.

''Now we feel like the ball is in their court,'' Gibson said.

Literally, and figuratively.