BOSTON -- Magic Johnson called it "a junior, junior, junior sky hook." New Englanders figure there couldn't be much worse -- or more unusual -- short of him also splashing tar on the Old North Church.

For 47 minutes 58 seconds Tuesday night, this fourth game of the championship series had followed what skeptics saw as the familiar NBA script: lots of wonderful basketball but little of true significance.

In tennis terms, both teams were holding serve. The Lakers had done it in their racehorse way in Los Angeles; the Celtics were replying in kind here, with their cerebral style seemingly all but assuring that the series would be tied at two games.

Anybody notice Kevin McHale limping Tuesday night? Did Danny Ainge and Robert Parish need stretchers by halftime? Whatever their ailments, the smart Celtics know how to play -- and when to play.

Or so it seemed.

That little mental edge of having to win was proving to the Celtics' advantage well into the fourth quarter, and especially after a surge fetched an eight-point lead with 3:29 left.

McHale's pregame wisdom was being played out in Boston Garden. The Lakers have a flair for increasing a 10-point lead to 20 in an instant, McHale had said. His Celtics are renowned for successfully nursing small leads at the end.

So what happened? Where did Celtics magic go, before Magic delivered the crushing blow for a three-games-to-one Lakers lead? The Celtics have been about as close to invincible here as pro games allow, losers only once in their most recent 38 games in Boston Garden and twice in the last 87.

"Defense," Johnson insisted. "Our trap was the key to it all. It got us more aggressive. And our offense got going good, started to flow."

Early on, it had been flowing all right. But backwards. The affair was typically Celtic, with their big men scoring well and rebounding even better.

And Ainge was being exceptionally versatile. He had not played well the first three games, what with having to contend with a six-inch height disadvantage against Johnson. Tuesday night seemed to be his revenge.

In addition to scoring 15 points in the first half, Ainge was competent on defense. (Johnson's 19 points in the half came mainly from the outside and the Lakers had few fast breaks.)

Even Ainge's misses were well-placed. On one, Johnson was tippy-toeing near the sideline after an Ainge clanger and tried to save the ball by bouncing it off Celtic Jerry Sichting.

Smart play.

Bad result.

As always seems to happen in Boston Garden, a ball that would go out of bounds 99 times out of 100 bounced off Sichting and stayed in play. In fact, it ended up in McHale's hands in a couple of seconds and in the basket a tick after that.

The plodding Celtics even were faster at times. Johnson would swish a long set, and then Ainge would beat him back and sink a layup off a baseball pass from Bird.

"When we're at home, and we're on the break," Lakers Coach Pat Riley had said of his team's problems running, "we've got a 10- or 12-point lead. Then those shots are okay. When you're on the road, and you're down, then you've got to be a little more conscious of the decisions part of fast-break basketball."

So at halftime Tuesday night, Johnson had just one assist; James Worthy was two for seven from the field and Kareem Abdul-Jabbar's sky hook was mostly a memory.

"LA Walks The Parquet Plank" read a sign, which also featured a skull and crossbones. Not even the most intense Lakers fan could argue.

"We're not doing lots of little things," Abdul-Jabbar had said after Sunday's loss here. "Like positioning for rebounds. How to rotate on the double teams. These are the little things that win basketball games.

"They had us looking around. They disguised double-teams well." So well, in fact, that Sichting Tuesday night slipped in and swiped the ball from Abdul-Jabbar as he was maneuvering against Parish.

Abdul-Jabbar had the startled look of a woman whose purse had just been snatched and the thief was dashing to safety. All of this had the Celtics firmly in command.

All that happened out of the ordinary was the teams throwing a few punches at each other. That seemed to signal that the nice-guy attitude of the opening three games was being replaced with serious knocking.

Worthy came up swinging after Dennis Johnson nailed him hard on a drive. That got much attention, with Worthy and Celtic Greg Kite being assessed double technical fouls. Unseen, on CBS at least, was Johnson cussing A.C. Green after the Lakers forward leveled Dennis Johnson in similar fashion in the first quarter.

At last, the series was generating some heat. But little suspense. Until . . .

The Celtics began to crack, ever so slightly. Michael Cooper filched the ball from Parish and nailed a three-pointer to narrow Boston's lead to 103-100.

"That broke our backs," Larry Bird said, "even though we were still ahead. If he had missed that shot, we would have won it."

They almost won it anyway, because Bird hit a magnificent three-point shot that gave Boston a two-point lead with 12 seconds left.

"I had the best view of it," Magic Johnson said. "I was under the basket -- and knew it was going in. I just said: 'My goodness. That's Larry.' "

He added: "We both do what we have to do to win games." His heroism was that running, semi-historic effort that clinched victory for the Lakers on their final shot.

Call it a fly hook.

"I didn't see it go in," Johnson said. "Somebody got a hand in my face as I released it."

"Well," said Riley, "the playoffs have just started." Or started to end.