PORT ST. LUCIE, Fla. — Perhaps it is nothing more than mind games, an intimidation ploy. But multiple industry sources told Newsday that the Royals have been quietly signaling their intent to seek retribution against the Mets on Opening Night.

It has been five months since Mets fireballer Noah Syndergaard added some spice to the World Series when he fired a fastball well over the head of pesky leadoff man Alcides Escobar to begin Game 3, the only contest won by the Mets.

But apparently, neither time nor a world championship has quelled the Royals’ lingering anger over the pitch, which Syndergaard maintained was part of a plan to establish the inner half of the plate.

The Mets open the regular season on Sunday night in Kansas City, with Matt Harvey facing Edinson Volquez. Terry Collins said on Tuesday that Syndergaard will start the second game of the season a week from today against Ian Kennedy.

Royals manager Ned Yost took exception to the idea that his team would retaliate in the season-opening series. “We haven’t even thought about it,” Yost said. “Our retribution was winning the World Series.”

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Even if the rhetoric proves to be empty, the message has come to the attention of Mets officials, though it had yet to filter into the clubhouse.

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A plunking in the name of revenge wouldn’t be out of the ordinary in such situations, especially since Syndergaard has embraced the furor that came in the aftermath of the incident.

Before Game 3, Syndergaard declared he had “a few tricks up my sleeve” to neutralize the Royals. During the game, Syndergaard reportedly told Royals catcher Salvador Perez that the pitch to Escobar had simply gotten away from him.

“I don’t remember saying that,” Syndergaard said this week.

Indeed, Syndergaard hasn’t altered his tone since Game 3, after which he challenged the Royals to take their complaints to the pitcher’s mound.

“If they have a problem with me throwing inside, then they can meet me 60 feet, 6 inches away,” he said at the time. “I’ve got no problem with that.”