Kristaps Porzingis’ day on Tuesday began with the news that he had been named NBA Eastern Conference Rookie of the Month for the third consecutive month.

It ended with him sitting for most of the fourth quarter because of ineffectiveness in the Knicks’ 97-89 loss to the Celtics at the Garden.

“I had a bad night,” Porzingis said.

Overall, Porzingis played 27:18 — the least by far among the Knicks starters — and just 5:11 in the fourth quarter. When the Knicks made a mini-run in the fourth to drop the Boston lead from 11 points to four with 7:37 left, Porzingis was on the bench.

That’s where he stayed as coach Derek Fisher decided to bypass the 20-year-old sensation. When Porzingis returned with 3:27 to go, the Knicks were down again by 10.

He immediately hit a basket, but the Knicks got no closer than eight in losing their sixth in seven contests.

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“It was a team situation,” Fisher said. “Third quarter, we came out flat. Couldn’t figure out a way to get anything going. Kris played a lot of those minutes in the third quarter. Got him out for a few minutes, got him back in to start the fourth quarter. Not much was happening good from that in terms of those five guys that were out there. It wasn’t about Kris doing good and bad. The five guys out there were not getting the job done, so we had to try and do some things differently. There wasn’t very much that worked tonight in terms of combinations of guys that would sustain anything on both ends other than maybe the first couple minutes of the game.”

Ah, those first couple minutes, when the Knicks shot out to a 9-0 lead. Boston answered right back, though, but the Knicks still led 47-45 at the half.

The warning signs were there. Arron Afflalo was the only Knick in double figures with 13 points. Porzingis had four.

Porzingis, who finished with 10 points and shot 4-for-11 with five rebounds and three turnovers, said: “I was missing a couple of shots at the beginning and I just couldn’t find my rhythm. That obviously didn’t help us at all . . . . At the end, that five that was on the floor we got back in the game, but we were trying to make another push and [the Celtics] were able to hold the lead. Once I came in, we didn’t have enough time.”

Speaking of time . . . . does Porzingis need some more on the bench because he’s hitting the dreaded rookie wall?

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“Not really,” he said. “Just a couple bad games. Physically, I’m feeling good. I’m preparing myself for games the same way. That’s the key.”