Jaylen Brown, right, and the Boston Celtics will try to slow down two-time NBA MVP Giannis Antetokounmpo when they play the defending champion Bucks in the second round of the playoffs. Jon Durr/Associated Press

BOSTON  — The Celtics’ sweep of the Brooklyn Nets in the first round of the playoffs underscored one thing about Boston’s late-season rise to the top tier of the NBA’s Eastern Conference: It was no fluke.

Leaning on the defensive brand cultivated under rookie coach Ime Udoka and punctuated by big scoring games by All-Star Jayson Tatum, Boston stymied a Brooklyn team that looked to be gaining late-season momentum, led by Kevin Durant and Kyrie Irving.

The only team to register a four-game sweep in the opening round, the Celtics are a conference-best 37-10 since their buzzer-beating loss to the Knicks on Jan. 6. They enter their second-round matchup with the defending champion Milwaukee Bucks playing their best basketball of the season.

Udoka said their performance against a high-quality Nets team that wasn’t a typical No. 7 seed bodes well for them going forward.

“We understood this is the playoffs and we’re gonna have to play really good teams,” he said. “The only thing we talk about is we’re a basketball team, not a track team. We’re not running from people.”

That includes embracing the challenge of trying to slow reigning NBA Finals MVP Giannis Antetokounmpo and the Bucks. The teams haven’t met in a postseason series since 2019, which Milwaukee won 4-1 in what proved to be Irving’s final games in a Boston jersey.

They split their four regular-season meetings this season, though they never met each other at full strength or with the Celtics’ post-trade deadline starting lineup of Robert Williams, Al Horford, Tatum, Jaylen Brown and Marcus Smart on the floor. That group is 27-7 together this season but hasn’t faced Antetokounmpo with the kind of reliable outside shooters he now has around him.

“We all know what Giannis is capable of, what he’s done, what he’s doing and what he’s gonna try to do,” Smart said. “For us, it’s gonna take another team effort. With those guys, he makes it really tough because of how aggressive he is and how he can get in the lane and not only create for himself, but create for those other guys. Those guys are sitting there ready for him to serve it up on a platter.”

The Bucks rolled to a 4-1 win over Chicago in the first round, but one player the Celtics may not have to deal with is Khris Middleton, whose availability for this series remains uncertain. The three-time All-Star hasn’t played since spraining the medial collateral ligament in his left knee 10 days ago in Game 2 against the Bulls.

Since Tatum and Brown’s first season together in Boston in 2017-18, Middleton has averaged 22.4 points and shot 52% from the field in two playoff series against the Celtics.

But Coach Mike Budenholzer said what he contributes on the defensive end is just as hard to replace.

“I do think he’s underrated in what he does defensively, including in big stretches of games, important moments, guarding the best wings,” Budenholzer said. “He takes a lot of pride in being a good defender. Also a little bit underrated, his size, he just does a lot of things, gets hits, gets rebounds, can start the break from a rebound. And he’s smart. He’s a good communicator. I think he helps guys out there. He sees and feels things at a high level defensively. There’s lots of things we miss on that end of the court.”

HILL UPDATE

Budenholzer said he remains hopeful that George Hill could return at some point during the series, though the 35-year-old guard isn’t expected to be available for Sunday’s opener. Hill missed the entire Chicago series because of an abdominal strain.

NO PAIN FOR WILLIAMS

Udoka said Williams didn’t experience any pain in his surgically repaired left knee after returning to the court for the final two games of the Brooklyn series.

The next step is getting his conditioning back before his minutes can return to normal.

“The wind, I don’t think, was quite there those last two games,” Udoka said. “You can scrimmage all you want, but there’s no way to really emulate that live game pace and action. So, to get his wind back up will be big this week. Just get some live work in the last few days and just get him built back up so he can get back to his normal rotation, lineups and minutes.”