It’s been almost two decades since the first time the Yankees played the Mets, and the common belief is that the Subway Series has long lost its original intrigue and luster. But then games like Wednesday night’s happen — games that remind everyone that when New York’s baseball teams go head to head, things can get very, very strange.

Take for instance, the fifth inning of the Yankees’ 9-5 win, when mild-mannered Mark Teixeira and soft-spoken Steven Matz nearly ignited the world’s unlikeliest brawl.

Matz plunked Teixeira in the left leg with one out in the fifth — after Teixeira hit a three-run homer to put the Yankees up 6-3 in the second. The Yankees’ first baseman shouted “Are you kidding me?” at Matz and stepped toward the mound, causing benches and bullpens to clear. Words were exchanged, both players were held back from going any further, no one was ejected and warnings were issued.

“I know Matz is a good kid,” Teixeira said. “When you hit a home run and the next pitch is not even close to the plate and hits you, it just looks bad.”

Teixeira slid hard into Neil Walker on a 1-6-3 double play one batter later. And, in case anyone thought the matter was settled, Hansel Robles got into a tense staredown with Teixeira in a bizarre situation in the seventh.

Robles thought Teixeira, standing at second, was stealing signs. Teixeira acted amused. Robles didn’t approve and jawed at Teixeira, standing on third, as he was walking off the mound. The dust-up added a bizarre chapter in a Subway Series anthology bursting with them.

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“I didn’t have his signs, I was breathing,” Teixeira said. “I was just trying to have some fun with him and he started staring at me more and more and yelling stuff. It was just funny. I think we all got a kick out of him. I’ve never gotten inside someone’s head by just standing there. It’s a talent, I guess. If you think I have your signs, just change them, don’t try to challenge me to a duel.”

Robles’ take: “He was trying to pick up signs. I got a little upset. That’s not the way you play baseball. You have to play baseball as a man.”

But that’s how things go when the Mets play the Yankees, when baseball becomes as much theater as sport. The Yankees won, so they got to be jovial. The Mets lost — and sent Yoenis Cespedes to the disabled list — and they were affronted. (Cespedes aggravated his strained quadriceps in his final at-bat.)

Even with all that, an actual baseball game was played at Yankee Stadium. Luis Severino (1-6) was brilliant in relief of starter Chad Green, allowing only a hit, a walk and an unearned run and striking out five in 4 1⁄3 innings. The Yankees scored three runs each in the first and second innings, and three in two-thirds on an inning against Robles in the seventh. The Mets continued their woes with runners in scoring position, going 2-for-12 and falling to a major-league worst .204. Walker hit a solo home run in the ninth.

Curtis Granderson kicked off the game with his franchise-leading 18th leadoff homer — right over the short porch he’s missed so much — and Walker and Cespedes hit back-to-back singles. Green walked Jay Bruce, and James Loney singled to left to bring in Walker before the Mets’ problems in the clutch bit them again. Michael Conforto struck out looking and Wilmer Flores’ weak grounder became4 a 6-4-3 double play.

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It would cost them immediately. Rob Refsnyder singled with one out in the first, Teixeira walked, and Chase Headley hit a double that Conforto bobbled near the leftfield wall. Refsnyder scored and Teixeira came around from first, balky knee and all. One batter later, Didi Gregorius doubled to right to give the Yankees a 3-2 lead.

The absurdities continued the next inning, when Kelly Johnson hit what should have been a groundout to first. Instead, it became a double when Teixeira misread the ball, ranging to the wrong side, falling and letting it skitter to the outfield. Rene Rivera singled to tie it at 3, but Teixeira got it all back in the second, when he blasted Matz’s sinker to rightfield for a three-run homer and the three-run lead.

Matz falls to 8-8, with a 3.63 ERA; he has one win in his last 12 starts.

“We know Steven Matz: He didn’t throw at anybody,” Terry Collins said. “By the way, if his command was that good, we wouldn’t have been behind 6-3. I thought Mark overreacted. That’s just my take on it. My issue is now every time somebody gets hit, all you’ve got to do is get mad and there’s warnings sent out. But we’ll leave it at that.”

Overreacted? Maybe. But what would a Subway Series be without a little drama?

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