The shine on the Mike Miller Era is officially off and Julius Randle was steaming afterward.

After getting blown out by powerhouses in Miami and Milwaukee, the Knicks figured to have an easy night playing the decimated Wizards. Several players admitted afterward they took their opponents too lightly — with Randle the most vocal and devastated by what transpired on a holiday-ruining night at the Garden.

Despite a frenzied late rally, the Knicks struggled in a pitiful humiliation against a G-League-type Wizards (9-20) roster that was missing eight players. After taking a 13-point lead in the first quarter, the Knicks (7-24) folded up and got tagged with an embarrassing 121-115 loss.

Several Knicks said they knew they were in trouble after a sluggish, unfocused morning shootaround.

“I think our approach the whole day was terrible,’’ said Randle, who finished with 35 points. “From shootaround on, we had a bad approach, myself included. We jumped out on them and didn’t sustain it. We were too relaxed. We weren’t as sharp and crisp as we need to be. I got to be better. We all got to be better. We got away with it at the beginning of the game. Eventually when we needed to stop a run we couldn’t and went down 17.’’

The Knicks made a late fourth-quarter surge, cutting that 17-point lead with 4:40 left to three points with 24.1 seconds to go. They even got the ball with a chance to tie, but Elfrid Payton missed a 3-pointer with 12 seconds left, the Wizards got the rebound and Troy Brown’s free throws sealed it.

The Knicks don’t play again until after Christmas — Thursday in Brooklyn.

“We have to look at the mirror and approach things after Christmas as true professionals as we’re supposed to, make sure we’re in a state mentally we do everything it takes to get a win,’’ Randle said. “We should never have been in that position [down 17]. How we approached the game was terrible. It can’t happen.”

Rookie RJ Barrett, who scored 13 of his 18 points in the first half, was unusually despondent — indicating the wretchedness of this loss.

“They out-hustled us and wanted it more,’’ Barrett said. “It’s very frustrating. We started off great and let it go. It hurts when someone comes in your house and outworks you.’’

Washington star Bradley Beal struck for 30 points, but the production of the unknowns did the Knicks in and placed Miller’s record as interim coach at 3-6.

Center Anzejs Pasecniks, a two-way G-League signee from Latvia, looked a little like his countryman Kristaps Porzingis in racking up 14 points on 6 of 7 shooting, mostly driving to the bucket.

Pasecniks is so obscure, the 7-foot-1 big man was spotted 2 ¹/₂ hours before the game with shopping bags at the players’ entrance, trying to convince security guards to allow him into the arena.

The laundry list of missing Wizards grew Sunday when guard Isaiah Thomas was suspended by the NBA for entering the stands to confront a heckler during a game in Philadelphia on Saturday.

But the Knicks couldn’t handle them anyway as Brown notched 26 points and Ish Smith added 17. Miller cited his team’s inability to handle Smith’s drives and allowing too many offensive rebounds.

“We didn’t play a consistent 48 minutes,’’ Miller said. “We didn’t have the urgency all the way through. We had urgency for pockets of the game in every quarter but not the entire quarter.’’

The lone bright spot for the Knicks was Damyean Dotson striking for 19 points to lead the late surge. But they couldn’t close the deal.

“We were a little sluggish — we felt those vibes this morning,’’ Dotson said. “These are the type of games we have to have. They had guys out and our focus went out the window.”

The Knicks played undisciplined basketball in the fourth. Early in the period, Bobby Portis committed a technical foul against his former team for being extra rough after the whistle blew while he was on the floor grappling for the ball with Gary Matthews.

Randle scored on his first four shots, including two 3-pointers and finished with 21 at intermission. Kevin Knox, making a rare start with Marcus Morris out with an Achilles strain, had eight points in the period but was blanked the rest of the way.

“Every team that comes in here has NBA players,’’ Miller said.

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