Nets forward Joe Harris drives to the basket against Celtics guard...

Nets forward Joe Harris drives to the basket against Celtics guard Jaylen Brown at Barclays Center on Sunday. Credit: Noah K. Murray

It had been more than seven long months since the Boston Celtics swept the Nets in the first round of the NBA playoffs.

Boston rode that momentum to the NBA Finals. Though the Celtics lost in six games to Golden State and then had to weather the season-long suspension of their coach, they entered Sunday’s game against the Nets with the best record in the league, the best offense in the league and an improved defense.

The Nets, meanwhile, endured a stormy offseason and a difficult start to the season, including a coaching change and an eight-game suspension of All-Star guard Kyrie Irving.

Heading into Sunday’s game at Barclays Center, the first between the teams since the playoffs, it appeared that the Nets had started to find their sea legs. Yet by the end of the game, it was clear that they still have a way to go before they can beat an elite team that seems to always have their number.

Jaylen Brown scored 34 points and Jayson Tatum added 29 points and 11 rebounds as the Celtics ended the Nets’ four-game winning streak with a 103-92 victory.

“That team had 103 points and we didn’t play our best,” Nets coach Jacque Vaughn said.

The loss dropped the Nets to 13-12. Boston (19-5) has won 15 of its last 17 games.

The Celtics were 15-for-38 from three-point range, which Kevin Durant said was the difference.

“The three-point line. They made six more than us,” Durant said. “If you look down across the board [boxscore], we were pretty much even in everything: rebounds, assists, turnovers the same, fouls. Then you look at the three-point line. They made one more shot than us and six more threes. They’re the best offense in the history of the league, right? 103 points. The three-point line killed us.”

The Nets might have been able to handle a big night from both Tatum and Brown if they could have come up with a more diversified offense. They still haven’t found a way to score that doesn’t involve Durant knocking down shot after shot.

Durant led the Nets with 31 points but had eight turnovers. His scoring helped cut Boston’s double-digit lead to two points midway through the fourth quarter. However, he got little support from his starting cast once Boston decided to double-team him, and the Celtics went on a 12-3 run to take control of the game.

“Just overall, we have to take advantage when teams double-team,” Vaughn said. “If you’re going to send a second guy at our best player, then we’ve got to make you pay for it.”

The stage was set for Irving to have a big night, given that it was announced before the game that Marcus Smart would sit out because of a left hip contusion he suffered in Friday night’s loss to Miami. Smart is the reigning defensive player of the year, and his absence should have opened things up for Irving.

Instead, he shot 7-for-21 on the way to his 18 points.

Joe Harris was the only other Net in double figures, finishing with 13 points and 5-for-10 shooting. The Nets got practically nothing from their bench.

“They’re a good team. You have to give them credit,” Irving said. “When you make costly mistakes down the stretches, it’s going to affect you .  .  . They make us pass and crowd the paint.”

The loss was just the Nets’ third in the last 10 games. It also was their first loss on this seven-game homestand, and they seemed a little stunned about what transpired.

Durant was asked if it made the team feel better that it had come down to three-point shooting.

“Nah,’’ he said. “We wanted to win.”

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