Boston’s Jaylen Brown shoots against the Warriors’ Draymond Green during the second half of Game 1 of the NBA Finals in San Francisco on Thursday. Brown scored 24 points in the Celtics’ 120-108 victory. Kyle Terada/Pool Photo via USA TODAY Sports

SAN FRANCISCO — As the fourth-quarter minutes expired and the Golden State Warriors kept missing shots, the Boston Celtics came alive to rally for a 120-108 win in Game 1 of the NBA Finals at Chase Center.

Not the ending the Warriors expected, not after yellow streamers rained from their roof to celebrate the Western Conference championship a week earlier.

How did they blow a 15-point, second-half lead?

Celtics Coach Ime Udoka pointed to Boston’s top-ranked defense, and a five-minute scoreless stretch by the Warriors backed up his claim. The Celtics went on a 17-0 run on 6-of-11 shooting (5 of 8 from 3-point range), while the Warriors shot blanks (0 for 5, 0 for 3) from the 6:04 mark to 70 seconds remaining.

“That’s who we’ve been all year: tough, grinders, resilient group that knows we can always rely on our defense to buckle down when we need it,” Udoka said. “… Didn’t have a great three quarters. Locked down when we needed to.”

Boston went on lockdown, specifically, with a smaller lineup that tried to force the Warriors’ shooters inside the 3-point arc. The Celtics switched up their man-to-man defense, and that foiled the Warriors, whose offensive rebounding keyed a 38-24 third-quarter swing.

“We wanted to get aggressive and go small, small, small,” Udoka said. “This is what we rely on all year, one-on-one defense.”

Said guard Derrick White: “We had to come together and slow them down. We changed defense up a little, made them work, got the stops. It was a lot of fun.”

Offensively, the Celtics overcame Jayson Tatum’s 3-of-17 shooting night and picked up the slack elsewhere, led by Al Horford (26 points), Jaylen Brown (24 points), White (21 points) and defensive master Marcus Smart (18 points).

“The guys kept finding me time after time, and also Derrick White made tough shots, too,” Horford said. “Get the looks, knock them down, that’s that.”

“That kind of blew the lid open for them,” Klay Thompson said of the Celtics’ 17-0 run.

Horford credited the fourth-quarter spark provided by Brown, who had 10 points in the opening five minutes of the fourth quarter.

Golden State’s offense dried up and resembled nothing like its opening-quarter outburst, when Steph Curry scored 21 of his 34 points.

“I was trying to ride that wave as long as I could,” Curry said. “They’re a good defensive team, but we created enough good looks offensively to win the game. We couldn’t get enough stops and let that lead get away in the fourth quarter.”

The Warriors tied an NBA Finals fourth-quarter record in getting outscored by 24 points, according to ESPN.

“When you’re making shots, that’s a boost. And when you’re missing shots, it’s a Debbie Downer,” said Draymond Green, who went 2 of 12 from the floor and 0 for 4 on 3-pointers. “They made them, we missed them.”

Another factor to the Celtics’ comeback: Opening-night nerves. All Celtics were making their career debuts on the NBA Finals stage.

“Everybody had nerves today from our side. It’s our first time being here,” Boston guard Payton Pritchard said. “Getting up and down, it went away quick.”

“Getting those opening-night jitters out, that settled as the game went on,” Udoka added. “We don’t expect (Jayson Tatum) to have a tough shooting night like that again. I don’t know if that’s attributed to their defense. It shows who we are as a team.”

Warriors Coach Steve Kerr credited the Celtics’ offense for the comeback, saying: “I mean, they made 21 3s. They were moving the ball really well, and they had us on our heels. They made a good push to start the fourth, and they kept that momentum going.

“Boston was – just played a brilliant quarter. They came in and earned the win.”

Smart said it was simply the Celtics’ season-long script.

“We’ve been counted out all year, rightfully so. We’ve had moments,” Smart said. “But we continue to fight.”

Tatum salvaged his off-shooting night with 13 assists. Afterward, he perhaps provided a pep talk for the Warriors.

“Our last two series, we lost Game 1,” Tatum said. “You’ve got to stay mellow, stay balanced, especially this early. It’s far from over. It’s one game. We have to be ready for them to respond. They’re going to come out and make adjustments. We have to be prepared.”

Brown said of the Warriors: “They played two bigs, (Kevon) Looney and Draymond, and they’ve been effective most of the playoffs. Looney dominated the offensive glass tonight, and Draymond is Draymond. We have to run our offense, make our reads and let the game decide itself.”