The Celtics bench has a down look while watching their season end on Friday night at Madison Square Garden vs. the Knicks. (AP photo)

BOSTON (AP) — The Boston Celtics entered this season with hopes of ending the NBA’s six-season drought without a repeat champion.

With a mostly unaltered roster led by All-Stars Jayson Tatum and Jaylen Brown, they looked like a team poised to do it after romping through the regular season and posting their second straight 60-win season while earning the No. 2 seed in the Eastern Conference.

But it all thudded to the surface in the postseason, cemented by Boston’s 4-2 conference semifinals loss to a New York Knicks team that it had previously dominated this season. The Celtics are now the sixth consecutive NBA champion to fail to make it out of the second round the following season.

Just as painful as getting dethroned at NBA champions was the devastating ruptured Achilles tendon injury to Tatum late in Game 4, which sidelined him for the final two games of the series. The 27-year-old is now staring at a rehabilitation process that will knock him out for most, if not all, of next season.

It casted a pall not only over the remainder of the New York series but has thrust the Celtics’ future into uncertainty heading into the offseason. That sentiment was clearly on Brown’s mind in the aftermath of their elimination as he tried to offer Boston’s fans some hope.

“This journey is not the end. It’s not the end for me. I look forward to coming back stronger. You just take this with the chin up,” Brown said. “I know, Boston, it looks gloomy right now obviously with JT being out, and us ending the year, but there’s a lot to look forward to. I want the city to feel excited about that. This is not the end.”

But it may not be that simple.

Boston’s payroll this season put it over the salary cap and will make them a luxury-tax team for the third consecutive season. It means they will be hit with a “repeater tax” penalty for being over the cap threshold in three out of four seasons.

With payroll for next season on track to come in around $225 million, next year’s tax bill would be at almost $280 million. The combined potential $500 million total price tag would be a league record.

It is unclear whether the team’s incoming ownership will want to keep paying those hefty penalties to maintain the current roster after agreeing to a purchase in March that is expected to have a final price of a minimum of $6.1 billion.

It could mean belt tightening in some fashion this offseason with 11 players currently under contract.

Tatum signed an NBA-record five-year, $314 million contract last July that will begin next season and pay him $54 million. Brown is playing under a five-year, $304 million deal that kicked in this season. He will make $53 million next season. That is followed by Jrue Holiday ($32 million), Kristaps Porzingis ($30 million), Derrick White ($28 million) and Sam Hauser ($10 million).

Of the top nine rotation players this season, only veteran Al Horford and Luke Kornet are free agents.

But there are concerns beyond the financial ones.

Porzingis’s health will also be in the spotlight after he was hampered throughout the latter part of the regular season and playoffs with a lingering viral illness that sapped him of strength and rendered him a virtual nonfactor against the Knicks.

Though he said he doesn’t think it will be a long-term thing.

“The best thing I need right now is just to rest. Just get somewhere in the sun and just let the rest of my system even itself out,” he said.

One positive sign is that he said he plans to still play for home country Latvia in EuroBasket this summer.

Then there’s Brown, who entered this postseason dealing with a right knee issue but was able to play through it. He has said he’s unsure whether it will require surgery this offseason.

Even with that uncertainty, Brown’s optimism remains high, although he acknowledged tough times may be ahead.

“Losing to the Knicks feels like death,” he said. “But I was always taught there’s life after death.”

“I thought they gave it everything they had throughout this season,” Celtics coach Joe Mazzulla said. “Obviously we didn’t achieve that, but you can’t take away from what they did and this is the price you pay for trying to go after something and that’s how it goes.”

The Celtics rolled to the NBA’s best record last season, but this time settled for the No. 2 seed in the East behind Cleveland. Still, Boston won 61 games, including a franchise-record 33 on the road, and was favored to defeat a Knicks team it swept in the regular season.

But the Celtics blew 20-point leads at home in both of the first two games, lost Tatum late in Game 4 when they were trying to tie the series, and never had a chance Friday to send it back to Boston for a decisive game Monday.

“We didn’t have the same team this year that we had last year,” White said. “Every year it’s a different team. We had a goal at the beginning of the year and we fell short.”

Perhaps things might have been different with a healthy Tatum, their leading scorer who figures to miss at least a good chunk of next season while recovering from surgery.

And perhaps a healthy Porzingis would have helped. He finished an awful series with four points in 11 minutes off the bench in Game 6. Plagued by the apparent re-emergence of a virus he had late in the season that saps his energy, he lost his starting spot in the series and never scored in double figures while logging more than 20 minutes only once.

“It was a tough challenge for me personally,” Porzingis said. “Ends on a bitter note like this, but we all have to go home and know that we left everything out here and then you can sleep at night.”