In that same game, Khris Middleton returned after missing the first 50 games with a hamstring tear that required surgery.
The Bucks lost that game to fall to 22-29, their season clearly in peril.
Don't look now, but Milwaukee is 17-7 since then and has won 13 of its last 16.
"They're really good," Celtics coach Brad Stevens said after the Bucks' 103-100 win in Boston on Wednesday night. "They've been one of the best teams in the East over the past month and a half. Since Middleton came back. So, I'm not surprised at their level, and their level is really high."
Wednesday night marked the Bucks' sixth attempt at rising to three games over .500. This time it worked as they held onto their tie for fifth place in the Eastern Conference.
"It's huge for us to continue our stretch of playing a high level of basketball," said Bucks rookie guard Malcolm Brogdon, who led the Bucks down the stretch. "It's huge for us to do it against this team at their home. It's a huge boost for our confidence. It's about continuing to play like this and not have content."
Milwaukee also knocked the Celtics from their one-day stay atop the conference as Boston, losing at home for the second time in 16 games and the first time in five on this homestand, dropped back to percentage points behind the Cleveland Cavaliers. Even worse for Boston, the Toronto Raptors are just a game and half behind the Celtics.
Brogdon, a second-round pick who has turned into a Rookie of the Year candidate, scored three baskets -- including a tough jumper with 3.9 seconds left -- and set up two others in the final 2:26 as the Bucks blew an eight-point fourth-quarter lead but evened their season series with Boston at 1-1.
"He's not a rookie. He's not a rookie," said Stevens. "And I say that with respect to him. Like that guy. Knows how to play."
Brogdon's reward was a water bottle shower from some teammates as he did a postgame television interview.
"He kept his composure -- he's done that all season for us," said Milwaukee coach Jason Kidd.
The game was tied at 93 when Brogdon chased down a ball deflected into the backcourt, picked it up with 11 on the shot clock and drove down the floor and scored. He then hit a floater in the lane and set up two baskets in a row before hitting the clincher.
The Celtics had the ball out of bounds with 3.9 seconds left, but Marcus Smart's off-balance heave off a deflected pass wasn't close.
As far as playing with more poise than your average rookie, Brogdon, who came out of the University of Virginia, said, "I think college has helped me. Playing four years of college you learn a lot about yourself more than anything. You have an identity to lean (on) and a strong foundation coming into the NBA."
Giannis Antetokounmpo led the Bucks with 22 points and nine rebounds, while Middleton had 19 points, six rebounds and five assists. Greg Monroe had 16 points and eight boards and Brogdon posted 16 points, nine assists and four rebounds.
"It's a great character test for us," said Kidd. "We've been tested all season. Understanding the ups and downs of an NBA season, it's about March and April playing your best."
Isaiah Thomas scored 32 points and broke Antoine Walker's club record of 222 3-pointers in a season. Jae Crowder led four others in double figures with 13 points -- with Avery Bradley posting 12 points and 10 rebounds.
Crowder, asked about the last Brogdon shot, said, "That's a tough shot. Avery was all over him. Very unfortunate."
Thomas tied Walker's record with a 3-point bomb on a fast break in the third quarter and then broke it with a heavily contested trey with 4:13 left in the game. It was Thomas' 223rd 3-pointer, and last of the game.
But the Bucks made life tough on him, and the Celtics didn't score a single point when he was on the bench in the first half.
"It's just a loss," said Boston's Al Horford, who had 11 points, six rebounds and six assists."
-- Celtics G Isaiah Thomas became the sixth Celtics player to score 2,000 points in a season. Larry Bird and Paul Pierce both did it four times, John Havlicek twice and Sam Jones and Kevin McHale once each.
-- Thomas extended his club record with a 3-pointer in his 50th straight game and also posted his 50th 25-point game of the season.
-- Guerschon Yabusele, the 16th overall pick in last year's draft, arrived from China and joined the Celtics' Maine Red Claws for their remaining games.