KANSAS CITY, Mo. — Baseball is a crazy game. Especially when you play a terrible team.

The bottom of the seventh began with shortstop Amed Rosario in left field for the Mets, and although that was a nervous moment for Rosario, who had never played outfield in a game before in his life, the Mets were not nervous.

That’s because they were comfortably numb, having scored six runs in the top of the inning to turn a one-run deficit into a five-run lead as the Mets went on to an 11-5 victory over the wretched Royals on Sunday at Kauffman Stadium, taking two of three in the series.

A sweep would have been nice, but after losing the first game Friday night, the Mets will take what they can get, knowing they return to the major league portion of their schedule come Tuesday at Citi Field against the Indians.

This was a gift win, much like all those Yankees wins against the Orioles.

“Rosey is just ridiculously athletic,’’ said slugger Pete Alonso, who set the NL rookie record for home runs with his 40th in the ninth inning. “Today in a panic situation, when we needed him out there, I thought he did well. So if we ever have a panic situation like that again, he’s going to do the job.’’

At this stage, every win is huge, and this victory embodied the Mets’ Next Man Up approach. Rosario was forced into left because J.D. Davis, dealing with a calf issue, came out of the game for a pinch runner in the top of the inning.

Davis came in as a pinch hitter in the top of the seventh for Aaron Altherr and did his job, driving a single past the Royals’ drawn-in infield that scored Todd Frazier to tie the game at 4-4.

Davis made his way to third on Tomas Nido’s double and represented the go-ahead run. Ruben Tejada came in to pinch run and scored along with Nido on Rosario’s single up the middle past a drawn-in infield.

That was the second time the Royals brought their infield in during the seventh and the second time the Mets burned them. The winning rally started because the Royals did not have a second baseman at that position against Frazier and he dropped a fly ball in short right against the shift for a double.

In the bottom of the inning, Tejada went to short and Rosario kept running to left field.

Rosario caught Whit Merrifield’s fly ball in the seventh and fielded a single to left as well. There had been talk early this year that Rosario could wind up a center fielder, though that talk is dead now because he is playing shortstop so well. But in these lean injury times with Jeff McNeil out with a hamstring injury, the Mets have to find a way to field all nine positions throughout the game.

“At first I was a little nervous, but once I started to loosen up, I was getting the hang of it out and once the ball was hit to me, I was comfortable,’’ said Rosario, who had three more hits on the day, raising his average to .291, and three more RBIs. “You can just imagine, I never played left field in my life before, so I was kind of nervous.’’

Rosario enjoyed helping out any way he could, but joked that on this sweltering day, it is a lot longer run to and from left field.

“It was hot out there,’’ he said through a translator. “I was already tired.’’

Rosario becomes the Mets’ ninth left fielder this season. When the seventh inning ended, he was greeted with high-fives in the happy Mets dugout. Rosario came to bat in the eighth and doubled in a run past first base, making him 1-for-1 as an outfielder.

Nine left fielders could be the answer to the question: How many Mets does it take to replace Yoenis Cespedes?

“Diversity helps,’’ Mickey Callaway said. “Sometimes you have to do whatever you have to do to win a game and that is what we did tonight.’’

The Mets moved to 64-60, two games out in the wild-card race, pending the Cubs’ night game against the Pirates. After an off day, it’s the Indians continuing their stay in New York City. Now it gets real.