Game 5 loss for Celtics will go down as one of the toughest in Boston sports lore

The Bucks' Jrue Holiday blocked a shot by Marcus Smart in the waning seconds.Jim Davis/Globe Staff

It is almost beyond comprehension.

It appeared certain the Celtics had this one. We saw 48 minutes of blood and thunder basketball between two worthy teams and there were electric moments in our fabled gym joint. There seemed to be no doubt the Celtics would take a 3-2 series lead back to Milwaukee with a chance to close things out and advance to the conference Finals.

The Celtics led by 14 in the fourth quarter. They led by 6 with 2:12 to go when Ageless Al Horford threw down a dunk after a Jaylen Brown miss.

And then the defending world champions showed you what they are made of and took back the night, beating the Celtics, 110-107, in what is surely one of the toughest losses in Boston sports lore.

“It hurts,’’ said Marcus Smart. “It definitely hurts . . . We just didn’t do what we were supposed to do. And when it mattered the most, they did . . . We know we did it to ourselves. Nobody else . . . We just fell apart down the stretch . . . But we don’t have time to sulk. It is what it is. On to the next one.’’

“Tonight was a tough loss, there’s no way around it,’’ said Jayson Tatum (34 points). “We got a game on Friday and what happened tonight is what happened.’’

In Boston-speak, this was a wicked blown opportunity. It belongs right down there with some of the stuff that always happened to the Bambino Curse Red Sox. It was a little like watching the Yankees come back after Pedro Martinez took a 5-2 lead into the eighth with a chance to win the American League pennant.

Please, let’s not having any blaming of the officials on this one. The Bucks earned their win and the Celtics paid the price for getting beat on the boards in the closing seconds. With the Bucks down 1 and 14.2 seconds left, Milwaukee’s Bobby Portis had a HUGE offensive rebound and put-back of a Giannis Antetokounmpo miss. The Bucks outrebounded the Celtics on the offensive glass, 17-5.

Milwaukee's Bobby Portis delivers the game-winning basket off a missed free throw late in the fourth quarter of Wednesday's playoff contest.Jim Davis/Globe Staff

Suddenly, the Celtics were behind by 1. And they were a disaster in the final 14.2 seconds, a study in miscommunication.

First Smart had his shot blocked by Jrue Holiday after Boston used its final timeout. Then Boston had to foul and fouled Arlington’s Pat Connaughton — a free throw machine. After the former St. John’s Prep star made two, the Celtics had no timeouts left, which meant they had to go the length of the floor, down 3, with 5.9 seconds left. Smart was stripped by Holiday.

And stunned silence in the Garden.

I saw Wyc Grousbeck on the parquet floor seconds after it ended.

“I’m still being positive,’’ said the Celtics owner. “I’ll be in Milwaukee and we’ll bring one home.’’

There is no other choice now. The Celtics have to win at the Fiserv Forum Friday, then come home and win again in a Game 7 Sunday Showdown. Otherwise, the Boston basketball season is over.

If it is over, Game 5 will be the one everybody remembers. Game 5′s pain will supercede the feel-good fourth-quarter moments of Game 4 in Milwaukee when Horford stood tall and the Celts played near-perfect basketball, making 16 of 19 shots and seemingly gutting the Deer.

The Celtics did not play a horrible game Wednesday. But regrets will run deep if they don’t bounce back with two wins.

They led by 14 in the fourth quarter. At home.

It doesn’t get much worse than that.

Jaylen Brown and the rest of the Celtics left the floor in disappointment.Jim Davis/Globe Staff

While we cry in our Boston beer, take a moment to give credit where it’s due. The Bucks are absolute menschs. They have no quit. They don’t complain to the officials. They just put their heads down and do what they do. Portis (14 points, 15 rebounds off the bench) plays like a dependable adult. Holiday (24 points) keeps shooting, even if they’re not going in. And Antetokounmpo is a worthy champion.

The Greek Freak, bloodied but unbowed at the finish, scored 40 with 11 rebounds. If it makes you feel any better he also was called for a couple of charges and got tagged with a traveling violation. That’s like watching a total eclipse of the sun. But it didn’t give the Celtics a win.

“The series is not over,’’ said Tatum. " . . . We knew coming in it was not going to be easy. They’re a great team. We knew that.’’

Earlier this week, it was announced the Bucks will play two preseason games in Abu Dhabi before the start of next season. When Bucks coach Mike Budenholzer was asked about this, he said, “We hope to take all the greatness that is Milwaukee and share it . . . "

The Celtics hope to experience all the greatness that is Milwaukee, win Friday, then bring it back to the Garden and win again Sunday.

It’s still possible. Just like the Bruins winning the Stanley Cup and the Red Sox winning the World Series is still possible.

But at this moment it feels impossible.