WASHINGTON — Marcus Morris came, scored and got kicked out in his Knicks preseason debut.

And now Morris could get suspended for the season opener in San Antonio — the club he reneged on this summer to sign with the Knicks.

Their volatile new forward who said he will bring “old-school Knicks’’ toughness this season backed up his words in a 104-99 preseason victory against the Wizards at Capital One Arena on Monday.

But his seemingly unnecessary antics on his team’s first offensive possession of the second half against Wizards’ Justin Anderson could cost him a one-game suspension and he sounded repentant afterward.

“It was just things said — I just kind of overreacted a little bit,’’ Morris said. “At the end of the day I never want to get thrown out of a game. There’s different ways to go about things and set a tone. It’s preseason. I’m happy it’s preseason. Things happen. It escalated.’’

Heating up from 3-point range, Morris finished with 17 first-half points before heading prematurely to the showers.

Morris committed an offensive foul by swinging the ball with his elbows flying near Anderson’s face, then literally bopped the ball off his head. To make matters worse, Morris, 30, initiated a post-whistle scuffle after Anderson clapped. Morris got in Anderson’s face as players from both clubs piled in to break up the scrum.

Morris, who often cites his toughness as being from “North Philly,” was given a Flagrant 2 foul, which carries an automatic ejection. An NBA official said all Flagant 2’s are reviewed for potential suspension and the penalty would be served at the start of the regular season.

That is a fact Morris did not realize.

“It’s preseason,’’ Morris said. “I’d be concerned if it was regular season. I wouldn’t want to miss any regular-season games. If it was regular season I wouldn’t have done that. My team needs me.’’

Morris fist-bumped a Knicks fan on his way out and wore a smile on his face throughout his long walk to the locker room. When told later — after he had met with the media — any suspension would not be served until for the regular season, Morris let out an expletive.

“It’s Marcus Morris,’’ Knicks coach Fizdale said. “Our team will embody his spirit, but he understands it can’t be to the detriment. He told me he didn’t want to hurt the kid and shouldn’t have made the play. At the same time, he does have an edge to him and we want to keep that edge.”

After a quiet first half, rookie shooting guard RJ Barrett found his way and Fizdale played the 19-year-old a team-high 39 minutes.

Without Morris on the floor, the No. 3 pick finished with 14 of his team-high tying 17 points after intermission, including two game-sealing free throws with five seconds to go. Barrett was 0-for-4 from 3-point range in the first half before connecting on two 3s in the final two quarters. Barrett was 6-for-13 from the field overall.

“He’s fearless,’’ Fizdale said. “The thing I was most proud of is how he competed defensively. Bradley Beal (five points in 16 minutes on 2-for-10 shooting) is one of the best 2-guards in the league and RJ took the challenge to battle him.’’

Morris said he “apologized’’ to his teammates and claimed Anderson said something to him to ignite his rage.

“It had to be something extra for me to do what I did,’’ Morris said. “It was a bad move and unprofessional. My team didn’t deserve that. But like I said in the beginning, we not taking no s–t.”