BOSTON — Call it a reality check: the Knicks never stood a chance. Jayson Tatum and Jaylen Brown, Boston’s All-Star duo, have been teammates since the Celtics selected Tatum third overall in 2017, one season after drafting Brown with the third pick. Al Horford has played alongside Brown for six seasons, with Tatum for five. Derrick White enters his fourth season at TD Garden, and the addition of both Jrue Holiday, a seamless fit in any lineup, and Kristaps Porzingis (out to start the season) elevated the Celtics 3-and-D identity even further. The same holds true for the Celtics’ bench: Payton Pritchard enters his fifth season with the team, while Sam Hauser is starting his fourth. This continuity is a crucial advantage — six of Boston’s core eight players have spent at least four seasons together, while Tatum and Brown have essentially been teammates their entire careers. This is why the Knicks were completely outmatched in their 132-109 season-opening loss to the Celtics on Tuesday, and why no one should have expected them to compete on Boston’s level so soon. The Knicks have a talented starting five on paper — Jalen Brunson, Mikal Bridges, Josh Hart, OG Anunoby and Karl-Anthony Towns. This lineup stacks up against the Celtics theoretically, but in reality, there’s a lot more work to be done. “Yeah that’s the easy way out,” Brunson said after the game. “But we still got our ass kicked. We’ve just gotta come out and see what we can do to be better. Yeah they’ve been at it for a long time, and we’re a fairly new team, but that’s no excuse.” Brunson is right. It’s not an excuse — it’s the reality. The Knicks, a team that won 50 games and secured the East’s No. 2 seed, chose not to stick with the formula that got them there. Instead, they made a gutsy move, trading three-time All-Star Julius Randle and sharpshooter Donte DiVincenzo to Minnesota three days before camp for Towns. Yes, the Celtics made their own bold moves — trading away Marcus Smart and Terry Rozier, plus gambling on Kyrie Irving, a decision that backfired with his departure in free agency. But they stuck with the Tatum-Brown duo. In fact, they doubled down on it, adding more defense (Holiday and White) and spacing (Porzingis) to complement their stars. The result? Repeated deep playoff runs followed by the 18th championship in franchise history. And now, a shellacking of the Knicks, a legitimate contender, via 37 points on 14-of-18 shooting from Tatum plus a tied NBA record with 29 threes made on Tuesday. “I think when you shoot the way they shoot, the numbers tell you how great there offense is,” head coach Tom Thibodeau said after the game. Thibodeau knew entering opening night that the Celtics boasted a level of cohesion and chemistry his Knicks couldn’t manufacture overnight. “And so you have to go into the game with the awareness — it’s going to create great effort on every play, great concentration. We knew that going in. You have to be strong defensively, and we have to be strong offensively. So that’s the biggest thing.” At least the Knicks got to see a living, breathing champion up close and personal. On the night the Celtics raised yet another championship banner and celebrated with their rings, they showed why they remain head and shoulders above not just the Knicks, but any team aspiring to take their place. The Celtics recorded 33 assists on 48 made baskets, junked the Knicks’ offense, and held Towns to 12 points and seven rebounds. Bridges struggled early, missing his first five shots before finding rhythm, while Brunson finished with 22 points and two assists, but well below his own expectations for the opener. “Personally I’ve gotta be better. Yeah. It starts with my approach and everything, and I’ve just gotta be better,” he said. “We can say a lot. We can dissect everything. They made a lot of threes. They probably made more than what we took. But we have to be better on both sides of the ball. I have to be better on both sides of the ball.” The Knicks can break down all the film they want, but real chemistry will only come with time under tension on the court. The Celtics have already put in the time, and it was the difference on Tuesday. “Obviously they’re a great team. That’s championship level basketball and I think for us it was a punch in the mouth,” said Miles McBride. “And we’ve gotta respond. Obviously it’s a long year, can’t overreact to one game, but I don’t think that’s how you go into a year and set the tone. I think we’ve gotta make sure that we get together and figure out what to do next.”