Boston Celtics Stun Golden State in N.B.A. Finals Game 1

SAN FRANCISCO — After a long and eventful road to the N.B.A. finals, Golden State was grateful for a full week to rest and recover before facing the Boston Celtics in Game 1 on Thursday night.

Golden State’s modest break came to an abrupt end. Boston made sure of it, stunning Golden State, 120-108, to take the opening game of the best-of-seven series at Chase Center.

The Celtics leaned on their depth to erase a 15-point deficit in the second half. Al Horford scored a team-high 26 points, while Jaylen Brown added 24 and Derrick White scored 21 off the bench.

Jayson Tatum scored just 12 points in the win while shooting 3 of 17 from the field, but he had a game-high 13 assists. The Celtics also managed to overcome a turbocharged effort form Golden State’s Stephen Curry, who scored 34 points.

Game 2 is Sunday night in San Francisco.

In remarks before the game, N.B.A. Commissioner Adam Silver noted how the finals was pitting two of the league’s original franchises — a fitting series for the N.B.A., which has been celebrating its 75th anniversary this season. The Philadelphia Warriors won the league’s first championship, all the way back in 1947, when they took care of the Chicago Stags in five games. The Celtics are chasing their 18th title, and their first since 2008.

The finals, of course, are familiar turf for Golden State’s celebrated stars. Curry, Klay Thompson and Draymond Green are making their sixth finals appearance in the past eight seasons. And the Warriors had looked familiarly dominant in needing just five games to eliminate the Dallas Mavericks in the Western Conference finals.

The Celtics, on the other hand, were coming off a bruising seven-game series with the Miami Heat in the Eastern Conference finals. Ahead of Game 1 against Golden State, Marcus Smart and Robert Williams III were still recovering from injuries. And Tatum and Brown, the Celtics’ two young stars, had been supplying huge minutes throughout the playoffs.

Golden State looked primed to jump all over Boston in the early going. In the first quarter alone, Curry sank six 3-pointers — a finals record for 3-pointers in a quarter — and scored 21 points as Golden State led by as many as 10. Even Andre Iguodala got into the act, supplying his first minutes since the first round after missing most of the postseason with back trouble.

But the Celtics are not in the finals by accident. They produced the league’s top-rated defense in the regular season, and they ramped up the pressure on Curry as the game wore on. Consider a single possession of the second quarter, as Curry tried to work himself free by coming off a series of screens. White defended him, then Tatum, then Smart, the league’s defensive player of the year. Surprise: Curry could not find an opening.

Jordan Poole closed the first half for Golden State by bricking a 3-point attempt off the top of the backboard, and the Celtics led, 56-54. A gold-clad crowd that had roared for much of the half seemed to be in a collective stupor. Adult refreshments awaited many fans on the concourse.

Golden State is famous for its explosive third quarters, though, and Thursday’s version of it was no different. By the time Curry threw in an acrobatic layup, Golden State was back up by 9.

But fueled by unsung players like White and Payton Pritchard, the Celtics mounted a huge run in the fourth quarter, taking a 109-103 lead when Horford sank back-to-back 3-pointers.

Fans began to file toward the exits in the final minute.