WASHINGTON — Only two games into the season, the Mets and Nationals dislike each other, and it’s unrelated to Max Scherzer switching sides in the rivalry.

Scherzer returned to his old stomping ground Friday night and received a warm ovation upon taking the mound. A night earlier, the Nationals had honored their former ace with a video tribute during pregame introductions.

The warm and fuzzy portion of Mets-Nationals is over.

Already angry about high fastballs that had plunked James McCann and hit Pete Alonso all too close to the face the previous night, the Mets erupted in the fifth inning, after Francisco Lindor hit the ground in the batter’s box. Lindor had been drilled in the protective jaw covering by Steve Cishek while squaring to bunt. 

Buck Showalter, irate, entered the field to voice his displeasure to plate umpire Chris Guccione. Mets players followed their manager from the dugout, and both benches and bullpens emptied. Cishek was ejected, but he later apologized to Lindor.

During the fray (which thankfully didn’t include much more than players brushing up against each other and yelling), Lindor arose without help and was examined by assistant trainer Joseph Golia. The shortstop departed the game, the latest Mets player to barely avoid a serious injury on a pitched ball.

The Mets announced X-rays were negative on Lindor’s jaw and he had passed concussion protocol.

“I’m proud of being a New York Met,” Lindor said after his team’s 7-3 victory at Nationals Park. “I got hit, I was on the ground, heard scuffles and looked up and my whole entire team was out there. My whole entire coaching staff was out there … that says a lot.

“I am super proud to be a New York Met and to be with this group of guys. I respect them a lot. I admire them and I am glad I am sharing the field with them every day.”

Thursday night, Alonso was fortunate Mason Thompson’s high-and-tight pitch in the ninth inning struck the protective jaw covering on his helmet after it skimmed his arm. Alonso escaped with a split lip. It might have been missing teeth if not for the plastic flap. McCann was also hit in the foot in the opener. Enough was enough with the Lindor plunking.

“The fourth one, I don’t even want to really hear about intent, if you are throwing up in there, it’s one of those things that can’t happen,” Showalter said.

These intra-division feuds can get messy. We saw it last year, when the Mets played in Philadelphia two weeks after Phillies reliever Jose Alvarado had drilled Michael Conforto in the wrist. Dominic Smith didn’t forget and began jawing with Alvarado, after the pitcher began pumping his fist to celebrate an inning-ending strikeout. Benches emptied.

If Scherzer had any temptation to retaliate against his former teammates, he resisted. Umpiring crew chief Mark Carlson was waiting for the right-hander when he returned to the mound for the fifth and issued Scherzer a warning.

Scherzer got the final laugh in that he beat his former team. His only blip was a mammoth two-run homer surrendered to Josh Bell in the fourth inning. Scherzer allowed three hits and struck out six over six innings. Considering there were questions this week over whether he would take his first turn in the rotation, following hamstring tightness, the Mets had to be happy.

That Scherzer’s Mets debut had to be attached to a beaning and benches emptying was unfortunate.

Scherzer’s significance to the club has only increased in the last week, after Jacob deGrom was diagnosed with a stress reaction in his right scapula which, in a best case scenario, will only keep him removed from the rotation until the end of May.

So until deGrom can return, it will be Scherzer’s turn in the rotation every fifth or sixth day that will carry most of the anticipation.

On top of that, there will be another 17 meetings between the Mets and Nationals this season. The animosity has just begun.