Knicks guard Jalen Brunson celebrates after scoring against the Boston...

Knicks guard Jalen Brunson celebrates after scoring against the Boston Celtics last April at TD Garden. Credit: AP/Steven Senne

BOSTON — On the floor at TD Garden for the morning shootaround Tuesday, their first time back here since May when they pulled off a series of upsets, the Knicks couldn’t help but think back.

The Knicks had three days off before Game 1 of the Eastern Conference semifinals arrived here last season, but in all of the meetings and planning, they never considered that the team’s moment would come by the worst imaginable situation.

TD Garden was going wild, Lucky the Leprechaun was leading cheers and dancing around the floor and the Knicks were 20 points down against the defending NBA champs after being swept in the regular season. You head to the locker room at halftime amid the deafening taunts and you have a choice.

The Knicks chose to make this their moment. Maybe chose is not the right word.

“That was not our strategy. We did not big-brain that,” Karl-Anthony Towns joked on Tuesday. “I know Thibs [Tom Thibodeau] is a madman with an amazing IQ. That was not one of the ideas. I think that Game 1 showed all the improvements that we made not only as players, as physical talents, but you know, mentally.

“Last year we were such a mentally tough team that nothing bothered us or wavered us. And the 20-point deficit against the champs and being in their home, that didn't matter to us. We keep fighting to the horn goes off.”

The comeback win in Game 1 was a shock and then history repeated itself in Game 2 — down 20 again and somehow pulling off another comeback victory on the way to advancing to the Eastern Conference finals. Mikal Bridges sealed the overtime win in Game 1 with a steal and then did it again in Game 2.

“We just kept fighting to the horn went off and found ourselves with the win and Mikal getting an amazing steal,” Towns said. “So didn't expect deja vu, but it was. And it showed that if you doubted us Game 1 we showed what we can do with the same situation. Obviously not favorable for us. Not something we wanted to be in. But it just shows the mental fortitude of our team.”

Moments like that can make a team. It didn’t save Thibodeau’s job as he was fired after the team lost in the conference finals to Indiana. The team returned nearly in full and maybe those lessons learned facing down the worst of circumstances are benefiting them now as they adjust to a new coach in Mike Brown and the new system in place — and the old expectations.

"We play for the New York Knicks,” Towns said. “There's adversity every day. So just going out there trying to win against a team that obviously has a championship under their belt and been together for a long time. For us, it's staying on the task at hand and doing everything we can to win the series.”

“Just understanding and adapting through a new system, a new coach, and for the guys not listening to noise,” Bridges said. “I know fans and stuff — I’m not saying all because I know a lot understand what a new system and a new coach does for players — how difficult it can be trying to learn, especially off past success. It’s different. It’s going to take some time. I think we’re learning and not paying attention to what others think and knowing that being here every single day all we’ve got to do is learn. It’s going to take growth.”

Tuesday marked the 20th game of the season and the Knicks have shown signs of that growth, adapting to Brown while he adapts to them, a system shifting — some of it forward and some of it returning to what was successful before. And they had a chance to show it again in Boston against a Celtics team that is far different than the one they knocked out.

Jayson Tatum is still sidelined from the torn Achilles he suffered in the series against the Knicks, Kristaps Porzingis is in Atlanta  again dealing with health issues, Al Horford is with Golden State and the Celtics still present some sort of ominous memories.

“Man, they still got the coach, coach [Joe] Mazzulla, and I think he’s a hell of a coach,” Bridges said. “They’ve got guys that are going to play hard, smart, a lot of talent. I know they’ve got guys banged up or not here, but they’ve got next man up and they come out playing hard, physical, and doing whatever it takes to win.”

The Knicks learned things here last year, lessons they believe will help them — on days like this and down the line.

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