Kristaps Porzingis attended the night session of the U.S. Open Sunday and looked noticeably broader than he did during the Las Vegas summer league.

The Post reported Monday the 7-foot-3 Porzingis has put on 11 pounds since returning from Latvia to train with the Knicks staff in late July. The Knicks drafted Porzingis fourth overall in last spring’s NBA draft.

“It’s the upper body,’’ Porzingis told The Post. “Guys can’t push me around that easy, and I still got time to get a little stronger. I can’t wait for training camp.’’

Porzingis confirmed he’s put on “five kilos’’ since late July — equivalent to 11 pounds.

“I’m working out twice a day, lifting hard, trying to eat as much as possible to gain weight, getting my sleep, doing the right things to gain weight,” he said. “I’m getting stronger and I’m feeling stronger playing in five-on-five pickup. Definitely feeling stronger.’’

Porzingis said he’s played five-on-five with Carmelo Anthony at Anthony’s new gym in Manhattan. The games have also included Knicks teammates Jose Calderon, Langston Galloway, Jerian Grant, Thanasis Antetokounmpo and area college players.

The Knicks open training camp in late September.