BOSTON — Well before the Boston Celtics ran away from Milwaukee on Wednesday night with a 38-18 third quarter and a 36-29 fourth, and well before Kemba Walker and Jayson Tatum combined for 22 points over the last 12 minutes, the team suffered from a slow start.

In the first half, Marcus Smart was propping up a sagging tent from both ends, filling in most of the defensive rotation on Giannis Antetokounmpo, and hitting a series of shots that kept the Celtics from going under.

Smart scored 11 of his 19 points and made three of his five 3-pointers in the first half, including an eight-point second quarter.

Smart’s shot-making ability, coming off a career-high .364 performance from downtown during the 2018-19 season, continues to grow. The sight of Smart keeping his team afloat Tuesday night certainly pleased a truly big shot maker, Kemba Walker.

“That’s who he is, man,” said Walker. “Over the years playing against that man, he’s just a tough guy. He never shies away from the moment. He made some huge shots. At one point, when we were all struggling, and he was the one keeping us in the game making all the right plays. He’s a tough guy, man. He works extremely hard, and he’s shooting the ball extremely well right now. We need him to continue that.”

Brad Stevens views Smart’s development as a delayed process, due to thumb surgery in March 2018. Smart returned on time to help the Celtics eliminate Milwaukee in the first round of the playoffs. But shooting with a bandaged hand needed patience, not to mention perspective.

“I definitely see the improvement now — dramatically for me,” said Smart. “With that thumb injury it’s tough, because the ball has to sit right there on your thumb. It was weighting there, so if I couldn’t hold a ball, it was hard to shoot it. The tape and everything. … Being able to recover to 100 percdent, to be able to shoot the ball fluently, to go through my shooting motion fluently, is big for my confidence.”

Nor did Smart finally recover with any changes in his mechanics or desire to launch.

“Nothing. I just continued to shoot it, just went back to it,” he said. “The weight bearing on my thumb prevented me from getting a full flick on the ball. Once my thumb got healthy it helped me even more.”

To the point, anyway, that Stevens can once again chart a dramatic rise in his point guard’s efficiency.

“As far as Marcus’ shooting, Marcus’ shooting has been on an upward trend ever since the hand thing a couple years ago,” said the Celtics coach. “After that year he had the thumb thing and everything else, I thought last year he shot it great and you kind of see that continuing.”

Walker has new appreciation, because he has always been on the other side against Smart. He has a good idea where Smart’s increasing efficiency is headed.

“He’s gotten better and better each and every year,” said Walker. “And you can see it tonight. He stepped up and made some huge 3-pointers. That’s what we need from him. We’re extremely confident in him. I’m extremely confident in him. I’m happy he’s my teammate and I want him to continue to shoot the basketball because he is a really good and he works hard at it. And it’s paying off. He shot 5-for-11 from 3, that’s amazing. That’s great. And I think he can continue to do that. And he will.”