MILWAUKEE — Even Doc Rivers couldn’t help but cast some doubt. He knows his Bucks have struggled to stay healthy this season. And before a rare game Tuesday in which his top three of Giannis Antetekounmpo, Damian Lillard and Khris Middleton were available, Rivers was optimistic about what his squad can look like at full strength but treaded carefully.

“Let’s see if we can get through the game,” Rivers said sheepishly.

Then, they didn’t. Late in the third quarter on Tuesday, Antetekounmpo crumbled to the ground while jogging up the court. The Bucks superstar left the game with a left calf strain and didn’t return. The Bucks handled the Celtics anyway, 104-91, at Fiserv Forum but the game marked something of a representation of how this season has unfolded atop the Eastern Conference.

As the Celtics – who have long clinched the top seed in the East – coast through the end of the regular season this week, it’s fair to ponder if they will receive a real threat in their path to the NBA Finals. The Bucks, though they now sit 14 games back of the Celtics, should be that team. Health, poor defense and a midseason coaching change have stood in their way. But Tuesday offered a reminder of how formidable the Bucks can be, that they can still be a challenger to the Celtics.

But they have to be healthy, and they certainly need Antetekounmpo, who left the arena after suffering his non-contact injury to get an MRI. Rivers described the concern level as “high.”

“But he’s Giannis,” Rivers said. “I think everyone probably feels the same way as I do right now. We’re just hoping for the best.”

With Antetekounmpo, the Bucks looked engaged. They looked motivated as they ended a four-game losing streak. Perhaps they were sparked by a lineup change, as Patrick Beverley started over Malik Beasley. They built a 24-point lead behind hot 3-point shooting and never looked back.

The shorthanded Celtics – without Kristaps Porzingis and Al Horford – looked disconnected and disengaged. Jaylen Brown scored just 14 points with five turnovers while going 7-for-19 and missing all six of his 3-pointers. Jayson Tatum led the way with 22 points, but the Celtics struggled mightily offensively as they scored a season-low 91 points. They shot 32 percent from 3-point range and didn’t attempt a single free throw.

Joe Mazzulla, who rested his regulars in the fourth quarter in each of the previous two games, opted to keep them in despite trailing by 20 in a game that didn’t hold meaningful stakes for them. They trimmed their deficit to 11 late in the third after Antektounmpo’s injury, but the Bucks had enough in the fourth to hold them off.

Other takeaways from the loss:

– Tuesday’s loss, in many ways, could just be chalked up to the Bucks simply being more engaged on their home floor and not missing. While the shorthanded C’s went 9-for-28 from distance in the first half as they missed several wide-open looks, the Bucks were playing with extreme confidence. They went 8-for-10 from 3-point land in the first quarter, and while Brook Lopez is a capable 3-point shooter, he had a somewhat out-of-body performance by making five of seven attempts in the first half. Meanwhile, the Celtics missed several wide-open looks, and it quickly snowballed on them.

– While the Celtics were busy bricking 3-pointers, one was made by an unlikely source: Luke Kornet. The 7-foot-1 center drilled his first 3-point attempt of the season late in the first quarter, and his “ice in the veins” celebration ensued as he backpedaled to defense. It was Kornet’s first 3-pointer since Game 3 of last season’s conference finals.

Almost ironically, as the Celtics struggled mightily shooting the ball, Kornet and Xavier Tillman combined to go 3-for-5 from deep in the first half.

– It didn’t help that the Celtics couldn’t get to the free throw line, as the Bucks were whistled for just one foul in the first half. Tatum seemed frustrated at a few no-calls after some of his drives to the hoop.

– With Kristaps Porzingis and Al Horford sidelined as they manage rest over the final week, the Celtics seemed to experiment with some lineups. At the end of the first quarter, they went to a small-ball lineup with Tatum as the tallest Celtic on the floor, and it had some success.