Boston Celtics’ Jayson Tatum (0) and Miami Heat’s Jimmy Butler (22) battle for a rebound during the second half of an NBA conference final playoff game Sunday, Sept. 27, 2020, in Lake Buena Vista, Fla. AP Photo/Mark J. Terrill

BOSTON — Jayson Tatum emerged as a bona fide star, Jaylen Brown showed he can be a consistent presence in the lineup and Kemba Walker helped the Celtics put the failed Kyrie Irving experiment behind them.

But following their Eastern Conference finals loss to Miami, it’s clear there is still work to do in Boston after the Celtics squandered their best opportunity yet under coach Brad Stevens to make it to the NBA Finals.

Stevens said he heads into the offseason lamenting only the outcome and not the effort by his players during the abnormal season.

“My regret is not what we put in. My regret is not how we prepared or worked or how hard our guys worked or how committed they were to playing and staying together,” he said. “You look back at those first couple of games (against Miami) and it put us in a tough spot. I just think that ultimately we had our chances and we didn’t take advantage of it enough.”

The Celtics returned from the COVID-19-caused hiatus and emerged as one of the hottest teams in the Florida bubble, winning five of their eight seeding games entering the playoffs.

They then swept the Philadelphia 76ers in the first round and held off the defending champion Toronto Raptors in seven games to advance to the conference finals — all without Gordon Hayward, who was sidelined in the opening game of the Philly series with a sprained right ankle.

Despite big efforts from Tatum, Brown and Walker, who all averaged 20 or more points per game in the playoffs, Hayward’s absence was felt in the back-to-back losses to open the series against the Heat, as the Celtics struggled to score against Miami’s athletic front line.

That combined with uncharacteristic lapses in defense contributed to them being unable to close out games in the 4-2 series loss.

But unlike in previous seasons, the issues were situational and don’t seem to be systemic. That’s something to build on for a team expected to remain a contender in the East next season.

“We got to use this fuel to fuel us to come back stronger, better, mentally, physically, emotionally, psychologically, all of it,” Marcus Smart said. “We’ve got to use it to our advantage to come back. It’s over. We can’t change the past. We can only get ready for the future.”

It’s also why Tatum said he doesn’t believe there needs to be wholesale changes.

“I believe in this group. I think we were capable. We had more than enough to get the job done. We just let a couple slip away,” he said. “A lot of guys got so much better this year and throughout the season, so much better from last season. So just to see guys continue to grow and get better, it’s a lot of fun. It was fun this year.”

GOOD FIT

Irving’s tumultuous two seasons in Boston almost unraveled the chemistry that president of basketball operations Danny Ainge spent building within the team’s young core.

But Ainge appears to have found his point guard for the foreseeable future.

Walker signed with Boston hoping to play in meaningful games. He seized that opportunity this postseason, averaging 19.6 points and 5.1 assists per game.

“You just have to learn how to grow,” he said. “We’re going to have to figure out how to win those games down the stretch. But we got time. … I thought we fought hard. That’s all you can ask for. I have a lot of respect for the guys that I play with.”

ROSTER MOSTLY INTACT

The Celtics are on good roster footing for next season, with only three potential free agents this offseason.

Hayward and center Enes Kanter both have player options, and the team must decide whether to pick up Semi Ojeleye’s fourth-year option.

Considering Hayward’s injury history, it’s unlikely he would give up a $34.2 million guarantee to test the free-agency waters. Kanter was solid off the bench but could go elsewhere in search of more than the roughly $5 million he’d make next year.

NEW DEAL FOR TATUM?

Coming off his first All-Star season, in which he led the team in scoring in both the regular season and playoffs, Tatum could possibly get a long-term deal. But he doesn’t become a restricted free agent until after next season, so there’s still time.

Tatum said he isn’t concerned about it.

“This was a hell of a year and I enjoyed it and I’m appreciative of everybody,” he said. “But at the end of the day, this was fun. I’m not really thinking about the other stuff right now.”