Giancarlo Stanton isn’t one to show much emotion, good or bad. He’s uncharacteristically cool for a 22-year-old, which could be the California in him. On Sunday, though, he couldn’t help himself. After striking out for a third time, he ripped the padded elbow protector off his arm and slammed it to the ground.

“I was pissed off today,” Stanton said.

As well he should be. Not only did Stanton go hitless at the plate, but he whiffed in the field, as well, overrunning a fly ball that was hit toward the line and allowing it to fall in for a double. What resulted was a five-run first inning for the Mets, who completed a series sweep over the Marlins with a 5-1 win.

“He had a bad game,” acknowledged manager Ozzie Guillen of his young outfielder, who has been the Marlins’ best offensive weapon this season when he has been healthy. “I like to see [anger]. At least he shows he cares.”

It was the Mets who most figured would be awful this season. But the Marlins are turning out to be the worst team of the two. They have lost eight of their 12 decisions with New York and solidified their hold on last place. If they don’t go better than 13-15 the rest of the way, they’ll end up with a record that will be no better — and perhaps worse — than last season’s mark of 72-90.

“Obviously, it’s not too much fun,” said Marlins pitcher Mark Buehrle, who took the loss. “Anytime you’re losing it’s not fun to come into work every day. But we’ve got to come in and finish strong.”

Buehrle gave up a grand slam to Jason Bay (who is hitting .160) in the first inning. But Buehrle probably deserved a better fate. After Ronny Cedeno doubled to start the game for the Mets, Justin Turner lofted a fly ball toward the line in right. Stanton hustled over to make the routine catch but suddenly reached back with his glove when he realized he had gone too far.

Too late.

The ball missed Stanton’s glove and landed in fair territory, as Turner raced into second with a double. Buehrle retired the next two Mets. But the Mets loaded the bases with two outs before Bay went deep to right.

“All hell broke loose in the first,” Buehrle said.

What caused Stanton to misplay the fly ball? Even he wasn’t completely sure. But he wasn’t the only outfielder having trouble making routine catches Sunday. Bryan Petersen in left also had difficulty with a couple of fly balls hit in his direction.

“Like, no clue,” Petersen replied when asked what made the going so difficult for outfielders. “It was like the air conditioning was blowing. ... It was just weird.

“Like, [David] Wright’s ball I thought was hooked, and it went left. And then Ike Davis’ ball I thought was straight, and it sliced. It was crazy.”

Was the air conditioning inside Marlins Park cranked up for the day game?

Guillen rolled his eyes at the suggestion.

“We were [wondering] the same stuff on the bench,” Guillen said of what might be the cause. “We looked up and the roof is closed. There’s no wind. Maybe the air conditioning was blowing a little bit too hard, because I couldn’t figure out what was happening there.

“We just played bad outfield [Sunday]. We’ve been playing here with the roof closed. We’ve played a lot of day games in the past. We didn’t look like we did out there [Sunday].”

Said Stanton of the outfield conditions: “It was a little different today.”

Not different was the Marlins’ continued sluggishness at the plate. After falling behind 5-0, they offered little threat against Mets pitcher Chris Young and a cast of relievers.

Asked if the Marlins have had problems dealing with adversity of late, Stanton replied: “Of late? All year. If we get down early, it’s tough to come back.”

Buehrle was close to unhittable after the first. He scattered only three hits over his next six innings on the mound.

But the damage had been done in the first with a pair of blows — Bay’s and, perhaps, the air conditioner’s.