Boston Celtics Beat Miami Heat in Game 7 for Trip to N.B.A. Finals

MIAMI — More than four months into a remarkable turnaround, the Celtics seem determined to keep it going. Behind Jayson Tatum and Jaylen Brown, the team’s two young stars, Boston is bound for the N.B.A. finals after defeating the Miami Heat, 100-96, in a decisive Game 7 on Sunday in the Eastern Conference finals.

Boston won the series, 4-3, and will face Golden State in the N.B.A. finals, starting Thursday in San Francisco. The Warriors, who are trying to resuscitate a dynasty that had been on hiatus, are pursuing their fourth championship in eight seasons. Golden State, the third seed in the Western Conference, will have home-court advantage over Boston, a second seed, because it had a better regular-season record, winning 53 games to Boston’s 51.

The Celtics won their last title in 2008, back when many of the best players on this year’s roster were elementary school students.

Boston opened Game 7 on a 9-1 run, and Miami spent the rest of the game trying to catch up. After one quarter the Celtics led by 15 points, and had held Miami to 17 points, 6 of them by Butler. When the Heat pushed back it was largely because of Butler. He scored 18 points in the second quarter and helped the Heat cut the lead to just 6 at halftime. But the Heat’s comeback attempt wasn’t enough.

Under Ime Udoka, their first-year coach, the Celtics have already engineered a comeback story of their own to remember. It was not until late January that they figured out how to defend, share the ball and win with any semblance of consistency.

In the postseason, the Celtics have eliminated a smorgasbord of N.B.A. luminaries and would-be contenders: the Nets, led by Kyrie Irving and Kevin Durant, in the first round; the reigning champions, the Milwaukee Bucks, in the conference semifinals; and, now, the top-seeded Heat, who withered in the face of the Celtics’ pressure.

All this after the Celtics had filled the first couple of months of the regular season with some of the most unappetizing basketball on the East Coast. Forget about contending for a championship: Could they even make the playoffs? They appeared in rigorous pursuit of rock bottom.

The Celtics began to plumb the depths early, in November, when a loss to the Chicago Bulls dropped their record to 2-5 and point guard Marcus Smart used his platform after the game to rip Tatum and Brown for hogging the ball.

By mid-January, a loss to Philadelphia had them at 21-22, and Joel Embiid, the 76ers’ star center, described Boston as an “iso-heavy team” that was easy to defend.

Even some of Udoka’s oldest friends were questioning whether he could unlock the team’s potential. Kendrick Williams, a youth coach who helped Udoka launch an Amateur Athletic Union team in 2006, when Udoka was still patrolling N.B.A. courts as a power forward, recalled reaching out to him via text message when the Celtics were struggling.

“And he was like: ‘Man, you know I’m not panicking. You know we’re going to get it right,’” Williams said. “He was so confident, it put me at ease.”

From the start of training camp — and even during his introductory news conference last summer — Udoka emphasized the importance of ball movement. It remained one of the staples of his film sessions as the Celtics labored with growing pains, and it was a message that eventually took root.

Before the Celtics faced the 76ers again in the middle of February, Udoka reminded his players of Embiid’s remarks. The Celtics went out and beat Philadelphia by 48 points for their ninth straight win.

“You can literally see the improvement of the ball movement,” Sixers Coach Doc Rivers said at the time. “The old Boston is more isos. This Boston is driving and playing with each other, and that’s what makes them so much tougher.”

But that was only one part of the Celtics’ winning formula. Led by Smart, who won the N.B.A.’s Defensive Player of the Year Award, the Celtics emerged as a ferocious group of defenders, their lineup bolstered by a pair of midseason acquisitions: Derrick White, a guard from the San Antonio Spurs, and Daniel Theis, a defense-minded center from the Houston Rockets who had started his career in Boston.

After winning 28 of their final 35 games to close out the regular season, the Celtics pulverized the Nets with a four-game sweep in the first round of the playoffs. Even before the series ended, Irving was telling reporters that the Celtics’ window was “now.” After the sweep was complete, Durant predicted that Boston had a chance “to do some big things.”

Boston and Miami traded wins over the first four games of the conference finals, then the Celtics became the first to string together two victories. Miami shot 33.3 percent in Game 4, then 31.9 percent in Game 5 — both lopsided defeats. But with their season on the line in Game 6, the Heat responded. Jimmy Butler scored 47 points on the road in Boston, forcing a winner-takes-all Game 7 in Miami.

On the road for this critical game, the Celtics delivered a winning performance worthy of the cheers of their fans who, not so long ago, had seen them at their worst. Now, perhaps, the very best is yet to come.