GREENBURGH, N.Y. — On an off night in which he played only 20 minutes because of foul trouble, Kristaps Porzingis still was the Knicks’ second-leading scorer with 14 points in Sunday’s 116-95 loss to Golden State.

But the focus for the rookie at Monday’s practice wasn’t on his offense. It was on the ways he needs to improve on defense after Draymond Green ran circles around him en route to a triple-double (20 points, 10 rebounds, 10 assists, 9-for-9 shooting).

Even Walt Frazier on the MSG broadcast noted that the 7-3 Porzingis seemed to have little lateral movement when guarding the 6-7 Green.

Call it another learning experience for the 20-year-old. He certainly did.

“I think I saw just how much better defensively I’ve got to be and know what type of team they are,” Porzingis said. “If my guy goes by me there’s no RoLo on the floor, don’t have a big guy that can help me. The paint was wide open. So those are the type of things I’ve got to know about the team and personnel.”

The defending NBA champion Warriors have given painful lessons to a lot of opposing players. Porzingis vowed to grow after his rough outing.

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“This is going to be a learning experience for me,” he said. “To make those two quick fouls and then sit out and later on try to not foul again and not be able to really play hard defensively because you don’t want to get fouled out . . . It’s just things I’ve got to learn and, as I get more experience, avoid those situations.’’

Green is eight inches shorter than Porzingis, but to the idea that there’s no way he can be expected to guard a smaller player, Porzingis said the Latvian equivalent of “pish-posh.” He expects to be able to do it. If not today, then soon.

“As I become a better defensive player and as I get more experienced, I’ve got to be able to guard him. If the basketball is moving in that direction, then I want to be on the floor in important moments and I want to be guarding him. So this is a good learning experience. I’ve got to use my length in those situations.”

Coach Derek Fisher said Porzingis is “really good at adjusting to what he sees. Every game that he plays, it’s another opportunity for him to gain more knowledge and understanding of how to play in this league, how to be successful every night. It doesn’t mean statistically successful, but just finding ways to positively impact your team. He generally does that. So even on a night where he gets in foul trouble, etc., there are a lot of times we’re still better having him on the floor than not. I think he’s good in terms of adjusting and adapting.”

What specifically did Fisher think Porzingis learned from Sunday? “Just that you have to be ready to play every night and that every night’s different,” Fisher said. “The matchups are different. The things that are going to be successful and/or cause you problems are going to be different each night. So it’s another learning experience for him and for our entire team, honestly, from that perspective.”

Knicks videos

Calderon returns to practice. Jose Calderon (groin) practiced and Fisher said it is “possible” that he will return tonight vs. Boston after missing three games. With Al Iannazzone

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