NEW YORK -- You can talk about the Knicks' poor assist total on Sunday (11) or you can dissect their reliance on isolation. But to Derrick Rose, New York's 119-114 Christmas Day loss to the Celtics came down to one thing.

"It was all defense, the way I look at it," Rose said shortly after New York's late comeback fell short. "We didn't communicate well."

That's one of the most troubling takeaways from a rough afternoon of basketball for New York. Issues on defense have hindered the Knicks' progress all season -- and cost them a game on Sunday.

Boston hit 39 percent of its 3-point attempts – including a flurry of 3s during a pivotal second-quarter stretch. And the Celtics scored an eye-popping 97 points over the final three quarters.

"It was all defense, the way I look at it," cited Derrick Rose as the reason for Sunday's loss to the Celtics. "We didn't communicate well." AP Photo/Seth Wenig

"Defensively, we weren't great tonight," said Knicks coach Jeff Hornacek.

Really, the Knicks haven't been great on defense for the majority of the season. If they don't figure out how to tighten things up, their issues on that side of the ball may keep them from doing anything of consequence this season.

Several defensive issues that have plagued the Knicks for much of the season surfaced on Sunday.

First, there was defending screens. More than one Knick cited communication issues in defending the pick-and-roll. Kristaps Porzingis said the Knicks need to do a better job of figuring when "when we want to switch and when we don't want to switch."

Defending the pick-and-roll is one of the toughest challenges a team defense faces in the NBA. So the Knicks aren't the only club that struggles in this area. But the Celtics screened for Isaiah Thomas, creating seams in the Knicks' defense and, ultimately, open shots.

The Knicks allowed the Celtics to catch the ball in areas of the floor where they were most comfortable. This was pointed out in the Knicks' scouting report, according to Rose, but wasn't executed properly. The result? Boston shot 52 percent on 2-point field goals.

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Of course, there were times when the Knicks didn't make any mistakes and Boston still came away with points. Thomas put pressure on the Knicks' defense all game, and Boston as a team moved the ball extremely well.

Thomas ended up with just four assists but often caused the Knicks' defense to tilt, which created an opening elsewhere. Whether it was Thomas or someone else, one of the Celtics ended up finding the open shooter. Boston finished with 25 assists on 45 made field goals.

The Knicks, on the other hand, had 11 assists on 41 makes. That's a low number, but it shouldn't come as a huge surprise.

With players who thrive in isolation like Rose, Anthony and (at times) Porzingis, the Knicks are never going to lead the league in assists. Boston also limited the Knicks' assist opportunities by defending well one-on-one and staying out of rotation.

So no one in the Knicks' locker room chalked Sunday's loss up to a lack of assists.

"I don't think that was a big issue today," Anthony said.

And he's right. The biggest issue was on defense. And if it isn't fixed soon, it will keep this Knicks team from accomplishing anything significant this season.