A group of mostly 20-something out-of-towners heading to Miami this time of year typically would be called spring breakers.

But for our purposes, we’re referring to the Boston Celtics. Their reward for outlasting the Milwaukee Bucks in a grueling seven-game Eastern Conference semifinal series is a date in the conference finals with the No. 1-seeded Miami Heat, starting Tuesday.

The series is a rematch of the 2020 conference finals, except then the Celtics had the higher seed and the games were at Walt Disney World — another spring vacation destination in Florida.

Many of the key characters are the same. The No. 2-seeded Celtics are once again led by their top guards, Jayson Tatum, Jaylen Brown and Marcus Smart, while the Heat will counter with their top stars, Jimmy Butler and Bam Adebayo.

But even though the rosters haven’t changed much, there are significant differences from two years ago. The Celtics are now coached by Ime Udoka, who morphed Boston’s defense into the league’s best in his first season. Boston’s Grant Williams and Miami’s Tyler Herro were rookies in 2020 and have since developed into indispensable role players.

Here is what to look out for in the Eastern Conference finals.

Wait. Before we get to that, wasn’t there something important that happened in the 2020 series?

Yes. At the end of Game 1, Adebayo blocked a Tatum dunk attempt that would have tied the score in overtime. It was one of the most important blocks in N.B.A. history and it changed the trajectory of a series that Boston was favored to win. The series was close: Three of the Heat’s four wins were by less than double digits.

How did each team do this year?

The Heat went 53-29, their best regular-season record since 2013-14, when LeBron James was on the team and they lost to San Antonio in the N.B.A. finals. This season provided their seventh highest win total in franchise history.

Boston finished hot on their heels. On Jan. 28, the Celtics were 25-25. Since then, including the playoffs, they’ve lost only nine times. They ended the regular season with 51 wins for a remarkable turnaround.

Both teams were strong defensively, but not as proficient offensively.

The playoffs are a different animal, though.

The Celtics opted not to try to avoid the Nets in the first round, even though that meant Kevin Durant and Kyrie Irving — two A-list stars — would await them. It turned out they didn’t have to worry. The Celtics swept the Nets, solidifying their status as a team to be feared.

Also in the first round, Miami faced the Atlanta Hawks, who employ one of the N.B.A.’s best guards in Trae Young. The Hawks were hampered with injuries, and the Heat easily dispatched them in five games, in part because of a suffocating defense on Young.

In the second round, the Celtics exchanged haymakers with the Bucks, who were missing a perennial All-Star in the injured Khris Middleton. The Celtics withstood 44 points and 20 rebounds from Giannis Antetokounmpo in Game 6, one of the greatest playoff performances ever. Tatum countered with 46 points to carry the Celtics to Game 7, where Milwaukee ran out of gas.

Miami caught a break in its semifinal series against the Philadelphia 76ers. Joel Embiid, the second-place finisher in the voting for the Most Valuable Player Award, missed part of the series because of a concussion and an orbital bone fracture. The Heat took the first two games at home. Embiid unexpectedly returned for Games 3 and 4 in Philadelphia, spurring two wins for the Sixers. But Miami adjusted and took the final two contests, and the series.

Who is favored in this series?

It’s a toss up. Miami has home-court advantage, but the Celtics were a different team in the second half of the season.

Both teams are strikingly similar in that they employ efficient, active, switching defenses, while occasionally struggling with offensive droughts. Both teams will have a welcome break from having to deal with a physically bruising center like Antetokounmpo or Embiid.

The Celtics have Tatum, who at 24 has blossomed into one of the most complete players in the N.B.A. He has also shown a penchant for delivering in big moments — like the 46-point performance against the Bucks, or his 50-point showing in a first-round playoff win against the Nets last year. During the regular season, Tatum averaged 26.9 points, 8 rebounds and 4.4 assists per game — all career highs. He has also improved at creating opportunities for teammates.

The Heat have Butler, a versatile six-time All-Star. He averaged 21.4 points, 5.9 rebounds and 5.5 assists per game during the regular season. In the postseason, Butler has been dominant, averaging 28.7 points, 7.6 rebounds and 5.4 assists in 10 games.

In addition, the Heat have the 22-year-old Herro, who averaged 20.7 points a game off the bench and was named the sixth man of the year. He can, every now and then, take over a game by himself. One of his best performances came against Boston in the 2020 playoffs, when he scored a career-high 37 points.

Any X factors?

Health, for one thing. The Celtics said Monday that Marcus Smart, their starting point guard and the league’s defensive player of the year, is questionable for Game 1 because of a foot sprain. The Heat’s starting point guard, Kyle Lowry, a six-time All-Star, is unlikely to play in Game 1 because of a hamstring injury. He’s missed most of the playoffs so far.

The Celtics’ starting center, Robert Williams III, will be available for Boston, a huge boost after he had missed most of the postseason because of a knee injury. His athleticism and shot-blocking skills will be a necessary counter to Adebayo.

The Celtics were buoyed by spurts of offense from Grant Williams, Al Horford and Payton Pritchard against the Bucks, while for the Heat, the third-year forward Max Strus has been a strong scorer off the bench.

Miami is slower and more methodical on offense than Boston and less reliant on 3-pointers. Heat guard Victor Oladipo, after missing most of the regular season recovering from an injury, has emerged as a playmaker in the postseason. He has reached double figures in scoring four of his eight playoff games.

Why will Boston win?

The best defensive team in the N.B.A. will limit Butler’s effectiveness. Because Butler is a weak 3-point shooter, Boston will crowd the paint and muck up Miami’s spacing. With the Williamses and Horford, Adebayo won’t be able to roam on defense as easily.

Also, Tatum is the best offensive player on either team.

Why will Miami win?

Miami is the more physical team, and Butler won’t be fazed by the Celtics’ defense. While his defenders sag off him from the perimeter, he is skilled enough to force his way into the paint and create space for shooters like Strus and Herro.

The Celtics will rely too much on deep 3s because of Adebayo’s strong rim protection and they’ll have cold shooting nights. Miami has the more reliable bench with Herro and Oladipo, a two-time All-Star. And if they need shooting in a pinch, they’ll dust off Duncan Robinson, who has been in and out of Miami’s rotation in the playoffs after starting 68 games in the regular season.

And if Miami doesn’t start off by winning games, Udonis Haslem, who has been on the Heat roster since the Big Bang, will yell at them until they do.