Here is the difference between an afternoon of fun and an afternoon of fury: A simple flick of the wrists, a baseball colliding with the beefy part of a bat, then soaring off toward the distant M&M’s and W.B. Mason signs in left field. A 2-0 game becomes a 6-0 game, and eventually an 11-1 victory, and a four-game sweep.

Wait till tomorrow to chew your nails to the quick.

“This,” Mickey Callaway would say after the Mets were done sweeping the Diamondbacks, “is the goal when you do things the right way, when you continue to grind. They should pay off at the end.”

It’ll take some time before we know if these 2019 Mets get that ultimate payday. What they have crafted for themselves is a September that gets more and more interesting by the day. They keep getting knocked down. They refuse to be knocked out. There are still 17 days of baseball season left, and they are two games shy of a playoff spot.

“It is a privilege to play games like this,” Juan Lagares said.

It was Lagares, without a Citi Field home run for more than two years, who delivered the day Thursday before a modest gathering of 21,856. His third-inning grand slam gave the Mets breathing room. His fifth-inning opposite-field shot turned it into a laugher. And whenever you can have a laugher in the saber teeth of September, you take it and run.

The news wasn’t all good. On the out-of-town scoreboard, the Brewers were jumping out quick against the Marlins, held on all day for a 3-2 win. That meant the Mets would get no closer on this day no matter how many runs they piled on Arizona, no matter what the Cubs did in San Diego.

Another win for the home team. But another day off the calendar, too. Such is the tenuous arithmetic of September. Such are the daily equations the Mets must calculate. Callaway admitted that he stole a few inadvertent peeks at the scoreboard “since it’s right there in front of you,” but insisted he was too consumed with the game in Queens to worry about one being played at Marlins Park, 1,097 miles away.

“I’ll know tonight,” he said, laughing.

The Mets have had one of the strangest seasons in their history, which is saying something. They have lost three games that were almost impossible to lose:

Sept. 2, the 11-10 calamity in Washington.

May 29, in L.A., a game the Mets led 8-3 in the seventh and lost 9-8 in the ninth when the Dodgers poked the first gaping hole in Edwin Diaz’s confidence, scoring four runs.

June 13, when the Mets led the Cardinals 4-2 with two outs in the ninth as torrential rains began to fall and instead of tarping the field the umpires let the teams slosh around long enough for St. Louis to tie the game. They won it the next day.

There have been no fewer than five different times when it was perfectly reasonable to declare their season dead, in order:

1) June 27, when the Phillies finished off a four-game sweep by disemboweling the Mets’ bullpen a third straight game; 2) July 12, when a loss in Miami dropped them a season-high 11-under .500; 3) July 21 when, after losing a third extra-inning walk-off in four games at San Francisco the Mets found themselves tied for 10th place — 10th! — in the wild-card standings; 4) Aug. 29, after the Braves and Cubs swept back-to-back series at Citi, dropping them to 67-66, five out of the wild card with 29 to go; 5) Sept. 2, the 11-10 catastrophe in DC.

And yet — here they are. Here they were Thursday, finally getting A-plus work out of Marcus Stroman, hitting six home runs (most ever for a home game), allowing Seth Lugo an extra day to keep his arm idle and iced, keeping pace with the Brewers, staying in the hunt for at least another day.

They get the Dodgers the next three days, and the Dodgers are right there with the Yankees and the Astros as the best teams in the sport, and the Mets almost certainly have to take two out of three before they head west on Monday for Colorado. There are 16 games left. How many do the Mets have to win? Eleven? Twelve? More?

“We need to win as much as we can,” Lagares said. “And right now, we feel confident every day that we’ll win that game.”

Here is the difference between an exhausted season and one still full of promise: an important game, an important win, and eyes wide open on the out-of-town scores. That’s the scorecard of a satisfying September, no matter how it plays out — and pays out — across the next 17 days.

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