Jayson Tatum clinched a memorable playoff win over the Brooklyn Nets with a Game 1 buzzer-beater and felt that moment was evidence of the Boston Celtics' progress this season.

The Celtics finished in the two seed in the East, meaning a daunting matchup with the Nets in round one after they progressed through the play-in tournament.

Game 1 was every bit as tricky as Boston might have feared, but they came through in dramatic fashion thanks to Tatum's last-gasp intervention.

It was Tatum who contested a Kevin Durant three after dogged Celtics defense, allowing Al Horford to grab the rebound and set in motion a flowing move in the final seconds.

Horford moved the ball on to Derrick White and then Jaylen Brown, who picked out Marcus Smart for what looked to be a make-or-break three-point attempt with the Nets still a point ahead.

Instead, Smart picked out a cutting Tatum for a spinning layup at the buzzer to claim a stunning 115-114 win at The Garden.

"I think we all thought Smart was going to shoot it," Tatum said. "Last-second shot, just crash the glass. If it doesn't go in, try to make a play.

"But when he took that dribble, we just kind of made eye contact and he made a great pass. I just had to make the layup.

"It doesn't get any better than that. A buzzer-beater in a playoff game at home."

Celtics coach Ime Udoka could have called a timeout when Durant missed but instead trusted his players to get the job done.

"You've got to give credit to Ime for trusting us in that situation with one timeout to just go," Smart said. "That's a big confidence builder for us.

"The coach trusted us to go out there and make a play and be basketball players."

The Celtics have come a long way from their start to the season, having been 17-19 at the turn of the year but 34-12 through to the end of the regular season – their .739 winning percentage third behind the Phoenix Suns (.787) and the Dallas Mavericks (.745) in 2022.

Reflecting on a win in which he scored a team-high 31 points – his ninth career 30-point playoff game and fourth against Brooklyn – Tatum said: "I think it just shows the progression of our team, how far we've come.

"In those first two months, obviously we were average and we were struggling. And we've just been playing the right way these last couple of months.

"And that's a reason why we've been so successful, especially in big moments. It's all about just trying to make the right play."

Smart added: "It was fulfilling for us, especially because of the way we started this year off; those types of games, we lost.

"We were probably crumbling, and for a moment there, it kind of looked like that was the direction it was going.

"But the resilience that we have, the approach we have, and the work we put in to make sure that doesn't happen – you just learn."