NEW YORK — Marlins reliever Anthony Bass’ slider sliced over the inner edge of the strike zone, catching the corner with relative ease. That much was not up for debate. As Mets outfielder Michael Conforto’s eyes locked on the baseball, he kept his feet planted to the ground and thrust his right elbow — whether intentionally or not, the world may never know — forward several inches. The ball grazed it, ricocheting into Miami catcher Chad Wallach’s mitt.

As home-plate umpire Ron Kulpa rose out of his crouch to begin signaling a called third strike, Conforto turned and pointed to his elbow, indicating that the pitch had hit him. Kulpa responded by animatedly tapping his own elbow to indicate that it was indeed a hit-by-pitch. Conforto jogged to first base, where Dominic Smith dumped a bottle of water on his head as the Mets mobbed him. Marlins manager Don Mattingly emerged from the visiting dugout to argue.

But it was too late. The Mets had won their home opener, 3-2, over the Marlins on a controversial walk-off hit batsman.

“Still kind of a little befuddled on what happened,” Wallach said. “I mean, we know what happened. He called it a strike and then changed his mind and called it a hit-by-pitch, so on that part we’re confused. I’ve never seen that before.”

Trailing after the sixth inning at Citi Field on Thursday, the Mets received new life when Jeff McNeil hit a game-tying homer off Bass to open the bottom of the ninth. They proceeded to load the bases on two hits and an intentional walk, bringing Conforto to the plate amidst the buzz of 8,492 fans — a raucous, sold-out crowd made up of the first fans to step foot into Citi Field for a game since 2019.

Two frames earlier, that same group had booed Conforto for hitting into an inning-ending double play that extended his early-season woes at the plate. This time, they tried to encourage him as he fell into an 0-2 count with one out. Conforto fouled off two pitches and took another for a ball, then Bass uncorked the slider that struck him on the elbow.

“It felt like it was coming back to me,” Conforto said of the pitch. “I turned. There may have been a little lift to my elbow just out of habit, out of reaction, and it barely skimmed the edge of my elbow guard. … I didn’t know what was going to happen after that moment. I knew there was going to be some controversy.”

In his postgame press conference, Conforto added that, “Obviously, it was not the way that I wanted to win the ballgame,” before repeating the same chorus over and over: “A win’s a win.”

For the Mets, that may be true, but for the Marlins, the loss was not a typical defeat. Mattingly did what he could to argue the ruling, triggering a replay review that confirmed Bass had hit Conforto with the pitch. That was the only aspect of the play eligible for review, leaving Mattingly — who felt Conforto had leaned into a similar pitch to reach base in the fifth inning — helpless to affect further change.

Major League Baseball Rule 5.05(b)(2) states that a batter is entitled to first base if he is struck by a ball he is not attempting to hit “unless (A) The ball is in the strike zone when it touches the batter, or (B) The batter makes no attempt to avoid being touched by the ball.”

Statcast data irrefutably shows that the pitch was in the strike zone, meaning a proper application of the rule would have resulted in a called third strike against Conforto. But umpires are human, resulting in 23 plays since 2008 in which batters were awarded first base on balls that hit them in the strike zone — an average of about one or two per season.

This one simply happened to occur in the most significant spot possible: bases loaded, bottom of the ninth.

“The guy was hit by the pitch in the strike zone,” Kulpa told a pool reporter after the game. “I should have called him out.”

Regarding the suggestion that he had purposely leaned into the pitch, Conforto noted that he was “in battle mode” with two strikes, and that he tends to hang over the plate to protect the outside corner in those situations. If he had leaned into Bass’ pitch, it was a byproduct of his approach, not some split-second decision to induce contact.

His reasoning didn’t leave the Marlins feeling any better about the outcome. After the game, pitcher Sandy Alcantara tweeted that the ruling was “unacceptable.” Wallach offered notes of confusion. Mattingly said he was frustrated because “you really can’t say [he] got hit by pitch … he got hit by a strike.”

The Mets, who had suffered through a season-opening series loss in Philadelphia before looking listless offensively for much of Thursday’s home opener, didn’t offer much argument to the contrary. They were only too happy to accept their good fortune in a walk-off victory.

“That’s what got us the win today,” Mets manager Luis Rojas said. “That’s why we’re celebrating. That’s why Michael got the right to go to first base.”

Marlins beat reporter Christina De Nicola contributed to this story.