New Knicks coach Jeff Hornacek had his trusty defensive coordinator at Quicken Loans Arena on Tuesday night for the season opener. Except Mike Longabardi no longer works for Hornacek, instead commanding the Cavaliers’ defense.

Longabardi, fired by Phoenix brass as a sacrificial lamb in December, received his championship ring after which Hornacek’s Knicks defense played like it did all preseason — awfully.

Longabardi, whom the Cavaliers hired in January, did well with Hornacek in Phoenix. The Suns were 13th in defensive efficiency their first year together in 2013-14, and 17th in 2014-15.

According to a source, Hornacek wanted to bring Longabardi, a native New Yorker, with him to the Knicks, but the Cavaliers wouldn’t let him out of his contract. It has left Hornacek without a defensive coach on his staff. Kurt Rambis remained as associate head coach and Jerry Sichting and Corey Gaines were brought in from his old Phoenix staff. Ex-Knick Howard Eisley was also added. But none focus on defense.

Defensive-minded center Joakim Noah doesn’t like what he sees so far with the club’s defensive cohesion. The club gave up 107 points per game in the preseason (27th) and gave up 69 points in the second half in Cleveland in Tuesday’s 117-88 embarrassment.

“We have to get better in every aspect of our defense,’’ Noah said. “One-on-one coverage, talking, game plan. Everything.’’

Game plan was a buzzword after the Oct. 4 preseason opener when the Rockets rang up 130 points. The players claimed there wasn’t one. Hornacek responded that only for the final two preseason games would he provide them with a defensive plan.

When offensive-minded Carmelo Anthony and Derrick Rose are worried more about the defense, it’s a big issue. The Knicks have off until Saturday’s home opener against Memphis to figure it out.

“I’m not worried about the offense, it’s defense for us,’’ Rose said.

After the debacle, Hornacek maintained the issue was the inability to stop Cleveland’s penetration, forcing the Knicks into scramble mode.

“Defensively we got to stop the guy with the ball and be more aggressive,’’ Hornacek said.

On the eve of the opener, Hornacek had talked about his defensive philosophy and concerns about the club’s doggedness in switching. It appeared the Knicks switched on most pick-and-rolls Tuesday, hanging Kristaps Porzingis out to dry against Kyrie Irving.

“If we’re going to switch, we got to do it with a little more determination and aggressiveness,’’ Hornacek said.

The Knicks coach, known for his high-speed offensive approach, says defensive game plans aren’t the end all, be all.

“The biggest thing, I played under Jerry Sloan [in Utah] — he just said basically ‘Just do it,’ ’’ Hornacek said. “We didn’t have a lot of rules defensively. We try to put rules in for these guys on what we want to do; however, they’re on the court. Sometimes they’re going to figure it out on the fly.’’

Instead, the Cavaliers figured out the Knicks and ran roughshod over them. The Knicks’ transition defense was poor. Porzingis looked befuddled. Anthony, who committed five fouls, looked a step slow.

“We couldn’t really get back on defense,’’ Porzingis said. “We didn’t do the little things we have to do to get those stops.’’

“I believe we’ll get better, I know we’ll get better, especially defensively,’’ Anthony added. “ I think more of our focus should be on defense now.”

Cohesion on defending the 1-4 pick-and-roll (PG-PF) was poor, according to Rose, in addition to closing out on shooters after doubling LeBron James in the post. Failure to levy a hard foul on James in the open court was also problematic, Rose said. Hornacek agreed that during the Cavaliers’ 20-4 third-quarter rampage, the Knicks didn’t foul enough.

“There’s a lot of room for improvement,’’ Rose said. “Communication is huge. Just letting everyone know what’s going on. We have a lot of room to improve.’’

Undeniably, not having their starting five together all preseason hurt chemistry on both ends. Hence, a bad start could be in the offing. Their first four games are against 2015-2016 playoffs clubs (Cleveland, Memphis, Detroit, Houston). The fifth game will be a beast — the War in the Windy City when Rose and Noah make emotional Chicago homecomings.

“I don’t want to make that excuse,” Anthony said of the disjointed preseason. “The guys that we had, we had. The guys we didn’t have, we didn’t have. We’re all together now. So practices are going to be shorter. There’s going to be more games than practices, so we’re going to have to really start getting better on the fly.’’