It was going to be a haymaker. Probably a death blow. The gut punch that turned a series and made its outcome seem almost inevitable.

And it was. All of that.

Just not in the way the Lakers or their fans imagined it. Not in their darkest nightmares.

Up 21 after a record first quarter, coasting by 24 midway through the second, ahead 20 with six minutes left in the third, the Lakers turned into passive and confused bystanders as Boston mounted the greatest comeback in NBA Finals history.

Celtics 97, Lakers 91, and this series is over.

Yes, they will play at least once more, on Sunday.

But you don’t lose a game like this and come back.

The Lakers just had their hearts ripped out. Their spirit broken. They will be doing well if they show their faces for practice today.

Add this one to the Lakers’ voluminous history of Celtics-green disasters.

In 1962, Game 7, Frank Selvy missed an open 10-footer that would have given the Lakers a championship.

In 1969, Game 7, Don Nelson’s shot hit the heel of the basket, went about six feet up and improbably fell through the net for the critical Boston points.

In 1984, Game 2, James Worthy threw away an easy inbounds pass, the Celtics won and the series turned.

And so on and so on. Eight Lakers defeats in 10 championship matchups with Boston. And a ninth only 48 minutes away.

Welcome to the pain, Next Generation of Lakers fans. Now you know what it’s about.

For 30 minutes of game time, it went as well as the Lakers could have hoped. Better.

Lamar Odom finally showed up. So did Pau Gasol. Kobe Bryant scored only three points in the first half, but it hardly mattered because everyone else in gold was pouring shots into the goal.

It was 9-2, 20-6, 35-14. And the Lakers had the biggest end-of-quarter lead in NBA Finals annals.

It was 58-40 at halftime, the Lakers were shooting 50 percent, and it seemed as if the Lakers were the team of destiny when Jordan Farmer banked in a desperate three at the buzzer.

Even halfway through the third quarter, the Lakers were up 70-50 on a pair of free throws by Vladimir Radmanovic.

They were about to humble the Celtics, show who was more athletic and more skilled. Instill some doubt in arrogant Boston minds. Put themselves in position to win a title on the Celtics’ home court.

Then the roof fell in. And the leprechauns tumbled into Staples Center.

It turned when Boston coach Doc Rivers went to a small lineup, sending in James Posey and Eddie House midway through the third quarter.

The Lakers had been ignoring Rajon Rondo and Kendrick Perkins, doubling the remaining Celtics shooters, suffocating them. But with Posey and House in the game, with the Big Three of Paul Pierce, Kevin Garnett and Ray Allen, the Celtics had scorers everywhere.

In a span of six minutes and change, the Celtics outscored the Lakers 23-3. The game was tied, the Lakers were reeling and Staples Center fans were speechless.

Celtics coach Doc Rivers said he knew the double-teams on his stars would end when his bench shooters began bombing in threes. Such as the two House made in the third quarter.

The Lakers never recovered.

Bryant attempted to turn up his game, while his teammates wandered in a fog, but couldn’t get it going. He scored 10 points in the fourth quarter, but finished with a series-low 17 points on 6-of-19 shooting.

Boston took the lead for good on an 18-footer by House with 4:02 left, followed by a reverse layup by Allen 45 seconds later. The Lakers got within two once, but that was it.

Perhaps the moment Lakers fans will remember with the clarity of a train wreck was Ray Allen going one-on-one with Sasha Vujacic, three-point game, 20 seconds to play … and Allen just blows past Vujacic for the clinching layup.

Said Phil Jackson: “Well, they just were into an open-floor situation, an open floor … and we have nobody to run and jump with that kind of (small) lineup. We had done it a possession, two possessions before, and Posey had hit a three. so we just said to the guys, stay home, take care of your guy, make him take a tough shot, and Allen was able to get by Sasha on that.”

And then came all the historical trivia, more fodder for Celtics triumphalism and Lakers defeatism.

Biggest comeback in NBA Finals history.

Biggest deficit after one quarter before coming back to win.

Biggest deficit at halftime, in the shot-clock era, before coming back to win.

OMG.

Just to cheer up Lakers fans, no NBA team ever has come back from a 3-1 deficit, not in the previous 28 times it has happened. Not that we thought the Lakers had a chance to do it, even before we saw that stat.

Kobe Bryant, again, summed up things best.

On the impact of the defeat: “I mean, we let a huge opportunity slip away, so I’m upset, hurt, disappointed. It’s a huge loss, no doubt about it.”

On how to deal with it: “A lot of wine, a lot of beer, a couple shots, maybe like 20 of them it, digest it, get back to work tomorrow. Nothing you can do.”

On being unable to kill off a team they had by 20 in the third quarter: “We just wet the bed. A nice big one, too, one of the ones you can’t put a towel over. It was terrible. Nothing you can do about it. They played great in the third quarter, we played like crap. They pulled out a great win, now it’s time to move on to the next one, period.”

Well, good luck with that. I’m thinking we just had some punctuation at the end of Game 4. A period, or “full stop,” as the English call it. What might have been a great series? It’s over now, except for one more round of shouting in Boston, probably Sunday night.