A big reason behind Miami Heat’s playoff success? Eye-opening fourth-quarter numbers.

The Miami Heat is doing many things well this postseason.

Quality ball movement, elite three-point shooting, a top-notch ability to draw fouls, and a much improved defense.

But the Heat wouldn’t hold an impressive 9-1 record this postseason — and a 1-0 lead over the Boston Celtics in the Eastern Conference finals — without its dominant play in fourth quarters during the playoffs. Game 2 of the East finals is Thursday at 7 p.m. (ESPN) at Disney’s Wide World of Sports Complex.

Miami owns a league-best plus/minus of plus-58 in the fourth quarter and is outscoring teams by 24 points per 100 possessions in final period this postseason. For perspective, the NBA’s top fourth-quarter team in the regular season (Oklahoma City Thunder) outscored opponents by 7.8 points per 100 possessions.

How a Bam Adebayo block pushed the Heat to a 1-0 lead in East finals. And other takeaways

The Heat’s fourth-quarter dominance continued in Tuesday’s overtime comeback win to begin the East finals.

“If you come in our locker room just a minute ago, a lot of us took a deep breath finally because the whole game you couldn’t take a deep breath,” Heat forward Jae Crowder said minutes after the dramatic Game 1 victory. “We had to always stay the course, always look forward to the next play and that was a tough one. We expect it to be like that from here on out. I mean that’s what it takes to be crowned in this league. It takes a lot of effort, a lot of guts.”

Miami entered the final period of regulation in a 12-point hole, and a Kemba Walker step-back jumper pushed Boston’s lead to 14 with 11:25 remaining in the fourth quarter. The Heat chipped away at the deficit and pulled within six points on a Duncan Robinson three-pointer with 8:59 to play in regulation before the Celtics responded with a 4-0 run to take a 10-point lead with 8:19 remaining in the fourth quarter.

From there, Miami took control and closed regulation on a 24-14 run to force overtime. In the extra five-minute period, the Heat outscored the Celtics 11-8 to hold on for the win with the help of one of the best defensive plays in recent playoff history.

With Miami ahead by two points, All-Star center Bam Adebayo emerged from the weakside and blocked Boston All-Star forward Jayson Tatum’s game-tying dunk attempt with 3.7 seconds remaining in overtime. Heat coach Erik Spoelstra said after the game that “sometimes when you have great competition like this, you just have to make plays that you can’t even really explain. That was Bam tonight.”

But the Heat’s other All-Star, Jimmy Butler, was important down the stretch, too. Miami’s max player stepped up late in Game 1 of the East finals, scoring eight of his 20 points between the fourth quarter and overtime.

Butler made a three-pointer with 22 seconds remaining in regulation to put the Heat ahead by one point before the Celtics tied it to force overtime. Then with Miami trailing by one point, Butler made a difficult and-1 floater over Tatum and made the free throw to put the Heat ahead by two with 12 seconds remaining in overtime.

Butler became the third player in the play-by-play era (since 1997) to make multiple go-ahead field goals in the final 24 seconds of the fourth quarter/overtime of a playoff game, joining Luka Doncic and LeBron James, according to ESPN Stats & Info.

The Heat is also the first team in NBA history to win multiple games after trailing by 10 or more points entering the fourth quarter during a single postseason, according to ESPN Stats & Info. Miami faced a 12-point deficit entering the fourth quarter of Tuesday’s win over the Celtics and a 12-point hole entering the final period in Game 3 of its second-round series against the Milwaukee Bucks.

“Some of the games have been close. Some of the games we’ve been up and the other team came back,” Spoelstra said of the Heat’s impressive fourth-quarter numbers in the playoffs. “I would like to see us be able to compete heading into the fourth where we’re not in a double-digit deficit, for sure.”

Defense was the catalyst behind Tuesday’s comeback, and not only because of Adebayo’s block that Los Angeles Lakers legend Magic Johnson called “the best defensive play I’ve seen ever in the playoffs.”

Over the final 12 minutes of Game 1 of the East finals (the final seven minutes of regulation and the five-minute overtime period), the Heat held the Celtics to 20 points on 7-of-22 shooting from the field and 1-of-8 shooting on threes. Tatum, who finished with a game-high 30 points, was 0-of-7 during that crucial stretch.

Meanwhile, the Heat scored 31 points while shooting 9 of 16 from the field and 4 of 8 on threes during this 12-minute span against a Celtics defense that has posted the NBA’s top defensive rating during the postseason.

“Spo is always positive,” Heat guard Goran Dragic said of Spoelstra’s message at the beginning of Tuesday’s fourth quarter. “He knows that we have a team who can make a run, as long as we defend well. I think our defense was solid, especially the last five minutes and in overtime. And from there on, just make the right play. We shared the ball. We made some open threes.”

Relief points also helped against an elite Celtics defense. Miami was able to get into the bonus midway through the fourth quarter and take 17 free throws to go with nine fast-break points between the final period of regulation and overtime.

Late-game excellence has become a part of the Heat’s identity this postseason.

Not only does Miami own the league’s top team fourth-quarter plus/minus in the playoffs, but the NBA’s three best individual fourth-quarter plus/minus numbers this postseason also belong to Heat players. Adebayo is an NBA-best plus-64, Dragic is a plus-61 and Butler is a plus-55 in the final period, with Crowder ranked seventh at plus-45 and rookie Tyler Herro tied for eighth at plus-39.

In addition, the Heat holds the league’s second-best offensive rating (scoring 122.3 points per 100 possessions) and third-best defensive rating (allowing 98.3 points per 100 possessions) in the fourth quarter this postseason.

But late-game execution wasn’t always a Heat strength.

Miami posted the NBA’s third-worst offensive rating (scoring 105.9 points per 100 possessions) and eighth-worst defensive rating (allowing 111.7 points per 100 possessions) in the fourth quarter during the regular season.

The Heat also owns a 6-1 record in “clutch” games during the playoffs after finishing the regular season with an 18-18 record in those situations. A “clutch” game is defined as one that has a margin of five points or fewer inside the final five minutes of the fourth quarter.

What changed?

The Heat’s defense has simply improved. After finishing the regular season with somewhat mediocre defensive numbers, Miami has recorded the fourth-best defensive rating in the playoffs.

Butler has also been one of the NBA’s top fourth-quarter options this postseason, averaging the second-most fourth quarter points in the playoffs among remaining players behind only Denver Nuggets guard Jamal Murray. Butler has averaged 7.2 points on 59.4 percent shooting from the field and 5 of 10 shooting on threes in the final period.

Butler has been efficient from all areas of the court late in playoff games. He has shot 10 of 16 from inside the paint, 4 of 6 from midrange and 5 of 10 from behind the three-point line in fourth quarters.

“That’s just his makeup,” Spoelstra said of Butler’s clutch play. “The moment is not too big for him. And he’s vulnerable enough to put himself out there and that’s why we have him.”

While Butler has earned the reputation of reliable fourth-quarter go-to option over the years, he has reached another level during the Heat’s playoff run. He averaged 4.6 points on 36.3 percent shooting from the field and 11 of 43 shooting on threes, and was a minus-47 in the final period during the regular season.

Also, Dragic is averaging 6.2 points on 46.2 percent shooting in the fourth quarter and Herro is 5 of 10 on threes in “clutch” situations during the playoffs (only Murray has made more “clutch” threes than Herro this postseason). Adebayo has limited those he has defended to 40.5 percent shooting from the field and 9 of 19 (47.4 percent) shooting from within six feet of the basket in fourth quarters during the playoffs.

On top of all that, the Heat has the NBA’s top fourth-quarter lineup in terms of plus/minus this postseason. The Dragic-Herro-Butler-Crowder-Adebayo combination is a league-best plus-33 in 27 fourth-quarter minutes during the playoffs.

Combine Miami’s defensive improvement and Butler’s emergence as one of the league’s most efficient fourth-quarter options with clutch moments from others on the roster, and it’s clear how the Heat has turned into the NBA’s best late-game team in the playoffs.

The question is: How sustainable is Miami’s late-game dominance, considering how big a turnaround it has been from the regular season and its absurdly good fourth-quarter net rating that would be almost impossible to maintain during a larger sample size of games?

With only three wins separating the Heat from an appearance in the NBA Finals and only seven wins separating the Heat from an NBA championship, it’s less about sustainability and more about survival at this point.

“I don’t think it’s just execution,” Butler said when asked to explain the team’s recent fourth-quarter success. “I think we’re in really, really, really good shape. You know, mentally, and whenever you’re not tired physically, you can concentrate. You can remember plays. You can do this and you can do that. We pride ourselves on that and I think as of late, we have been playing great basketball. Now we just have to do it for the entire game.”

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