When Francisco Alvarez stepped to the plate Monday in the eighth inning, you couldn’t blame the Mets’ catching future if he had more on his mind than White Sox reliever Cam Booser.

The slumping Alvarez certainly has noticed the uptick in playing time for understudy Luis Torrens, including the final back-to-back games of the Dodgers’ series, largely because of his own offensive struggles. And Alvarez’s loosening grip on the starter’s job hardly was a secret, as manager Carlos Mendoza made a point to speak with the 23-year-old about the situation over the weekend, encouraging him to use the breather to work on things in the batting cage.

If all that wasn’t weighing heavily enough on Alvarez’s shoulders, there were his first two at-bats Monday afternoon, when he hacked at a pair of first-pitch sinkers from Mets castoff Adrian Houser, turning each into routine groundouts.

The lack of patience was understandable for a high-ceiling prospect currently hitting to his floor, and every at-bat is a referendum on his increasingly fragile lineup status. But for a slugger like Alvarez, just as the bad swings can establish a narrative, so can the productive ones, which is why his leadoff single in the eighth inning played such a massive role in the Mets’ harder-than-it-should’ve-been 2-1 victory over the White Sox at Citi Field on Memorial Day.

Alvarez’s hit turned out to set up the tying run, later delivered by his pinch runner, Luisangel Acuna, who scored on Juan Soto’s sacrifice fly. Francisco Lindor belted the walk-off sacrifice fly in the ninth, but he credited Alvarez’s hit with waking up the Mets.

“He started that, it was a huge at-bat,” Lindor said. “One of the biggest in the game, if not the biggest.”

The Mets had only three hits and zero runs off Houser into the seventh and wound up leaving the bases loaded that inning. So with six outs left to avoid the humiliation of losing to the 17-win White Sox, it was up to Alvarez, in the No. 9 spot, to ignite some spark of hope.

He was an unlikely candidate, batting .232 with a .625 OPS since his return from a broken hamate bone, including a 2-for-27 funk (.074) leading up to that eighth inning.

Before the game, Mendoza wasn’t shy about mentioning the youngster’s trouble with fastballs — a pitch Alvarez typically crushes — and how it is one that needs to be solved.

“I just feel like they’re throwing fastballs by him,” Mendoza said.

The stats definitely supported the manager’s argument. A year ago, Alvarez crushed heaters at a .315 clip with a 22.1% whiff rate, compared with a pedestrian .250 and a worrisome 40.9% this season. Those are very concerning performance dips. So with the evidence piled up against him, Alvarez responded Monday — in a pivotal spot — with one of his better ABs to date.

He took the first four pitches, a called-strike cutter followed by two changeups outside the zone, then another cutter for strike two. Finally, Booser tried to put him away with a 98-mph fastball, just off the bottom inside corner, but Alvarez smacked a 110-mph single through the left side of the infield. There was relief as much as celebration on his part.

“It’s a good feeling,” Alvarez said.

Said Lindor, “It’s one of those where you see him fighting. You see his demeanor, like he wants it. He’s a guy that shows every emotion. And getting that single was huge. It gave the rest of us, like, ‘Ah, here we go.’ It’s going to happen.”

The Mets were anxious to see that from Alvarez, who renovated his entire swing approach during the winter, then had the process interrupted midway through spring training with the fractured hamate bone in his left hand, a particularly bothersome injury for hitters.

Alvarez returned only a month ago after 10 rehab games (two at Triple-A Syracuse), so it’s possible he’s still getting up to speed with just 81 plate appearances to date.

When asked specifically about his fastball issues, Alvarez shrugged off the question.

“It’s still early in the year,” he said. “It’s not the time to talk about the numbers right now. I think we’ll talk about the numbers at the end of the year, September, if I don’t hit the fastball.”

Spoken like someone who believes this is just a temporary blip along the way, even if the Mets’ confidence had begun to fray to a small degree, based on the team’s search for offense earlier this month.

With Mendoza juggling the lineup in an effort to scrape up whatever runs he could, it was logical to eye Alvarez’s job as vulnerable, especially with Torrens’ surprising production (.267 batting average, .762 OPS).

Even Monday, after Alvarez was removed for Acuna, Torrens took over behind the plate in the ninth and was in the middle of the game-winning rally. After Tyrone Taylor’s leadoff double and an intentional walk to Jeff McNeil, it was Torrens who smoked a single to leftfield, hit so hard (108 mph) that Taylor had to be held up at third base.

Lindor then ripped the next pitch for the deciding sacrifice fly, kicking off the party with his jubilant teammates. But Alvarez finally grabbed a share of the spotlight, too. The Mets would like him to do so in more of those moments.

“It was a good sign that he got to a good fastball and he was able to put the barrel on it,” Mendoza said. “But that’s where it starts. Getting on time allows you to make some good swing decisions.”

And justify the manager’s decision to keep him in the lineup as much as possible.