Jayson Tatum and the Boston Celtics won a seven-game battle with the Toronto Raptors to reach the Eastern Conference finals, while their opponent, Miami, upset the No. 1 seed. Mark J. Terrill/Associated Press

They have been the top defensive team in the NBA playoffs through two rounds, allowing an average of 100 points in 11 games.

The Celtics also rank first in opponents’ field goal percentage at 41 percent and 3-point shooting at 31 percent, and Boston kept the defending champion Toronto Raptors under 100 points in all four of its second-round victories.

That defense will need to continue to be top notch in order for the Celtics to make it through the Eastern Conference finals and advance to the NBA finals for the first time in a decade.

The third-seeded Celtics open the conference finals Tuesday night at Disney World against the fifth-seeded Miami Heat, a team with plenty of scoring options and a surprising 8-1 record in the playoffs.

The Heat arrive in their first conference finals since LeBron James left in 2014 averaging 112.1 points in the playoffs, hitting 14.1 3-pointers per game at a 38 percent clip.

“Guard them as hard as you can,” Celtics Coach Brad Stevens said after practice Monday. “They’re excellent cutters. They’re physical cutters. You’ve got to get low. You’ve got to make it as tough as possible.

“You’ve got to be willing to tip your hat and say, ‘Great shot,’ and move on on a couple of those plays. This is probably the closest team in the East that we’ve seen to the Warriors with regard to their cutting and shooting.”

The Heat have been led in the playoffs by Jimmy Butler (21.8 ppg) and Goran Dragic (21.1), while versatile big man Bam Adebayo scores 16.2 points per game, and rookie Tyler Herro is averaging 14.7 points off the bench.

Former Celtics forward Jae Crowder, acquired in a February trade with the Memphis Grizzlies, scores 12.8 points per game, and Duncan Robinson is a 3-point threat who averages 10.6 points.

Crowder has a team-best 30 3-pointers in the playoffs, followed by Robinson and Dragic (24 each) and Herro (22), and the Heat get to the basket as well.

“They never stop moving, so you never can relax or let your guard down,” said Jayson Tatum, whose son, Deuce, and mother, Brandy Cole-Barnes, will be in attendance for the series. “You’ve got to stay locked in.

“Both teams are here for a reason. I expect it to be a lot of fun. It’s going to be tough. For us, everything starts on defense. We’ve got to focus all our attention on energy there to begin with.”

The Celtics, making their third appearance in the conference finals in the past four years, lost to James and the Cleveland Cavaliers in 2017 and 2018.

The Celtics, who are expected to get Gordon Hayward back from a sprained right ankle this series, can reach the NBA finals by continuing their strong defensive play.

“Those guys are going to be ready, so are we,” Kemba Walker said. “It’s going to be a fight. It’s going to be fun.

“We’ve got to do it all for a very long time, especially defensively. They have so many different ways to score the basketball. We going to be real locked into their shooters, real locked into Jimmy, obviously. Bam’s a different kind of big who can do pretty much everything.

“We’re versatile, and so are they. We’re going to have to figure ways out to get stops consistently.”

The Celtics held the Raptors to 94 and 99 points in winning the first two games of the second round, 89 points in a Game 5 rout and then just 87 points with the season on the line in Game 7.

Marcus Smart will probably be spending plenty of time on Butler in what will be a key matchup.

“There’s so many different ways they can hurt you,” Stevens said. “Miami can beat you in isolation. They’re one of the best cutting teams I’ve seen, obviously great from behind the 3-point line. They’ve got a number of guys that can go for 25 or 30 in a given game.

“(They’re) super organized, so when they sense a weakness, they’re going to pick on it. They’re really good. We just have to do the best we can and make it as difficult as possible. Easy for me to talk about, harder to execute.”

The Celtics and Heat have met three times, with Miami going 2-1 in series that were held in 2010-12.

As for Hayward, who was injured in Game 1 of the opening round against the Philadelphia 76ers, Stevens said the forward is improving.

“He went through a hard workout, what we call our small-group workouts after practice,” Stevens said. “He looked good when he was going through it, but there’s a big difference between doing that and actually getting into a game. He’s getting better.”