KANSAS CITY, Mo. — Overreacting to Opening Day is a yearly ritual and silly.

If winning the first game were a bellwether of what was to come, it would be the Mets even more than the Yankees who would be the symbol of championships. After all, the Mets went into Sunday night 35-19 in openers, the .648 winning percentage a major-league best.

But they only have two championships. The Royals are why they do not have three.

If you want to cull meaning from this opener, it was that the Mets received yet another firsthand account of what it is going to take to be the last team standing. The Royals used the first nine innings of 2016 to restate their mission statement of pesky offense and lockdown defense.

They are the baseball version of Floyd Mayweather in the ring — they artistically take your will away, not with knockout skills but with a relentless barrage of excellence. They look good. You look bad. They outpoint you.

The Mets were made to stand on the third-base line for an extended period in the pregame to watch videos of last year’s World Series and the raising of the championship banner at Kauffman Stadium. If that were not enough, the Royals then went out and déjà vu-ed the heck out of the Mets.

Yoenis Cespedes butchered a ball, Lorenzo Cain had a timely walk, and the Royals put the ball in play with metronome frequency and took extra bases and defended exquisitely. Jab, move. Jab, move. Jab, move.

“Obviously they are the champions, not just of the American League but all of baseball,” Travis d’Arnaud said. “It is nice to have that challenge given to us right at the beginning of the year.”

The final score was 4-3, and it was that close because shockingly, the normally impenetrable Royals bullpen wobbled, particularly new addition Joakim Soria, who yielded three eighth-inning runs. The Royals relievers allowed eight of the first 15 Mets they faced to reach before Wade Davis whiffed David Wright and Cespedes with the tying run 90 feet away to close the game.

“They are tough to beat,” Terry Collins said.

Indeed. The Mets now have lost five of six to the Royals dating to the World Series — in three of those losses, Edinson Volquez started against Matt Harvey. Volquez is a grade or two down from Harvey in skill, but the Royals just excel at team offense and team defense, which raises the performance of the whole group.

On defense, Volquez got out of men-on situations in the second, third and fourth innings thanks to superb plays by third baseman Mike Moustakas, first baseman Eric Hosmer and catcher Salvador Perez. Meanwhile, Cespedes’ first-inning drop led to one run, and Juan Lagares’ inability to shoestring an Alex Gordon sinking liner that would have been the third out in the sixth instead led to two runs and Harvey’s ouster. Harvey’s stuff was not his best, but it still was fine, yet he struck out only two of the 25 Royals he faced.

“They do a good job of putting good pitches in play,” Harvey said.

Hosmer is the Royals’ cleanup hitter. In the first, he defied a shift by grounding an RBI single to the opposite field, where the shortstop would normally play. He helped fuel the two-run fifth with a bunt single. Again, he is the cleanup hitter.

“You can’t give them many opportunities,” Collins said.

The Mets manager has been redundant and adamant about putting last year away to focus on a new quest in 2016. In a way, revisiting the Royals does that because what the Mets were offering against the best in baseball was not good enough last year and — stronger than Collins’ words — there it was in living color and real time Sunday night.

This is what the Mets are pursuing — a persistent style that does not waver, that resonates against any foe. Perhaps they have that with their starting pitching against pretty much any club except for a Royals team that, like Jimmy Connors in his prime, can return any serve, no matter the speed. The Mets are dreaming big, and the Royals are a reminder of what it is going to take to be the last team standing.

The Mets can play imperfectly against the Braves or Phillies and still conquer. But the Royals are a different weight class. This is the weight class in which the 2016 Mets are determined to play.

That the Mets are 0-1 is irrelevant. That they still are looking up at the Royals, however, may not be.