BOSTON — In snatching a 2-1 lead in their Eastern Conference semifinals series, the Milwaukee Bucks demonstrated so much of what’s gone right about their season.

They also sputtered through a stretch late in the game during which things most definitely went wrong.

The list of happy things stretched long: Giannis Antetokounmpo was the best player on the floor and in Kia NBA MVP contention mode as he scored 32 points with 13 rebounds, eight assists and three blocks in Milwaukee’s 123-116 victory over the Boston Celtics Friday night at TD Garden.

Fans and viewers got a glimpse of the Bucks’ scoring potency when, coming out of halftime, they posted the first 40-point quarter of this series. The defense that coach Mike Budenholzer demands was especially evident in limiting Boston to 14-of-36 shooting in the second half. Then there was Milwaukee’s deep rotation and trust in reserves – guards George Hill (21 points) and Pat Connaughton (14) led their bench’s 42-16 scoring advantage.

The down side came near the end, when Milwaukee’s late-game execution was so poor Budenholzer didn’t even want to talk about it in front of the cameras and microphones afterward.

He preferred to wait until Saturday, when he could directly address his players while they review video of Game 3.

“I’ll save it for film tomorrow,” Budenholzer said. “It’s not very smart. It’s not very good. That’s the great thing for coaches … we’ll find more things where we can get better. We just touched on one of them for sure.”

What happened was, the Bucks opened a fat lead – 17 points in the fourth quarter – and squandered much of it. They did it in the most damaging way possible, too, by sending a parade of Celtics to the foul line to score with the game clock stopped.

With 4:51 left Milwaukee was up 114-97, more than doubling the eight-point edge they held when the final period began.

With 1:20 left, that lead was down to 118-111, whittled down by Jaylen Brown’s fast-break layup and the Celtics’ perfect 12-for-12 from the line in that stretch. Many of the fans at TD Garden were heading to the exits, even as the Bucks appeared to be heading for trouble.

You wondered if some might wind up knocking to get back in, à la the Miami fans who bailed on the Heat before Ray Allen’s famous 3-pointer saved Game 6 of the 2013 Finals.

Those late minutes of the fourth quarter seemed to last an eternity, and that was just for spectators and viewers. It felt twice that to the Bucks’ players and coaches.

I think it’s part of the growth of this team, learning how to deal with those type of scenarios and situations.

Bucks center Pau Gasol

“It was [long],” said Pau Gasol, the veteran All-Star watching these days as an inactive player on Milwaukee’s roster. “But I think it’s part of the growth of this team, learning how to deal with those type of scenarios and situations.”

It wasn’t just that the Bucks were burning through their lead. It’s that Boston was energized watching their late scramble pay off. Al Horford sank six free throws in the run; Jayson Tatum, four; and Gordon Hayward, two.

“On the road, that gets a little dicey,” Connaughton said. “Whenever a team gets a little life at the end of a game, especially when they cut a [17-point lead to seven], that’s never a fun thing. But I think the way we were able to withstand it and make a bucket here or there to nullify what they were doing at the free throw line was good.”

Said Gasol: “The Celtics are trying to rush possessions, trying to rush you into bad decisions. So you have to be patient, hold the ball, understand the possessions and get a good shot. Don’t turn it over. We didn’t do a very good job of that at the end.”

Step by step, point by point, the Celtics were gaining hope. So … much … time … left.

Gasol’s analysis from the side? “We were very aggressive tonight defensively. And at the end, we weren’t able to turn it down and play smarter. We kept that pressure on, and that led us to commit silly fouls or unnecessary fouls, and put them at the line when we didn’t want them there. The experience in your brain has to tell you to be smarter.”

Milwaukee did manage a few high notes during the low period: Hill pounced on an offensive rebound to steal a basket. At 118-105, Antetokounmpo blocked Kyrie Irving’s fast-break layup to save two points and stifle a sure crowd explosion.

“I don’t think we were really concerned,” said center Brook Lopez. “We just tried to keep our foot on the gas. Keep that intensity. They drew some fouls and made some free throws. And then they had the little funky 1-3-1 defense, whatever that was. They were trying to trap a little. We’ll look at that [on film].”

This is not about nitpicking. This is about focusing on the growth still available to a Milwaukee team with lofty ambitions.

Antetokounmpo was special. The Bucks were stingy enough on defense. But when they talked about playing their game for 48 minutes, they should have ‘fessed up on the three-and-a-half of those that nearly bit them.

The Celtics ran out of time – only 10.6 seconds remained when they got within five, 121-116. And Antetokounmpo, who missed six of his first 20 free throws, didn’t miss his final pair.

The Bucks, in essence, earned the ability to swoon by padding their lead early. But their close out was less than optimal, which is probably not how Budenholzer will put it in closed quarters.

“We know they’re not going to quit,” Lopez said. “So we’ve just got to stick with it the entirety of the game. I know it’s a boring answer, but Game 4, we’ve got to do the same thing.”

Maybe not exactly the same.