PHILADELPHIA — The Mets had a decision to make Saturday night about their lineup against left-hander Cristopher Sanchez: Use center fielder A.J. Ewing, a left-handed hitter, against one of the best southpaws in baseball, or stack the lineup with right-handed hitters at the expense of outfield defense.

The latter choice was what they went with, starting utilityman Eric Wagaman in right field and moving Carson Benge to center, where Ewing usually plays. Ewing is hitting just .194 against left-handed pitching this season with a .437 OPS, and the other left-handed options in right field weren’t great either. Jared Young is hitting .125 against lefties this season, and Brett Baty is hitting just .175 against them.

Wagaman cost the Mets a run in right field, getting to a line drive late and catching it on the ground for a single. One can hardly blame a bench player playing out of position for a 15-3 loss, but it did call into question the Mets’ decision-making when it comes to their two rookie outfielders, Ewing and Benge.

“There’s been some tough matchups there, especially some tough left-on-left out of the bullpen, and there’s been times where he stays in there and he gives you good at-bat,” said manager Carlos Mendoza. “But then there’s been times where he chases, and I think that’s part of the development at this level, facing left-handed pitching. Not only starters, but relievers in high leverage situations.”

The Mets have been somewhat strict with their platoon decisions this season, opting whenever possible to play the splits instead of the hot hand or the green rookie. Benge got the same treatment early in the season.

Ewing, a 21-year-old out of Ohio, understands why the Mets are protecting him from some of the tougher left-on-left matchups. He doesn’t deny that he’s chasing pitches out of the zone. At times, he’s found himself feeling tense in the box against lefties, maybe even a bit overeager.

“It’s about being comfortable in the box,” Ewing told the Daily News on Sunday at Citizens Bank Park. “Feeling comfortable in the box is big for me and that’s an adjustment I’ve made over the last couple of games.”

Ewing has recognized his shoulders tensing and his upper body going stiff. That doesn’t lend itself to proper mechanics or pitch selection. His arms end up too high, and his hands in the wrong position. What he’s trying to do is remind himself to take a breath and relax his upper body, let his shoulders drop to their proper position to be able to use his legs and go about his at-bats as he usually would.

Ewing is looking at more pitch data to see where lefties are locating their pitches against him and is taking reps off the pitching machine. It’s not something he’s especially worried about, since he knows chasing pitches can come with inexperience. It’s part of the development of every young hitter, and his overall numbers show that he’s adapting to the Major Leagues quite well.

“I’m just going to keep playing,” he said. “Every opportunity I have against left-handed pitching, I’m going to try to take advantage.”

At this point, Ewing should probably be playing every day. They won’t be able to shelter him forever, and they believe this is just part of his development. But at the same time, the Mets are still trying to win, which means they have to put the best lineup out on the field every day, and if Ewing is struggling against lefties, he may not be the best option.

One school of thought is that he has to play through it. Given the other options, the Mets might be inclined to let him do that in upcoming games against left-handers, but it’s tough to tell.

Regardless, Ewing is happy with how he’s handled himself in the Major Leagues while continuing to develop and learn. He’s gone through stretches at the plate where he’s looked overmatched regardless of which side the ball is coming from, and he’s managed to get himself out of those periods each time.

The thing about the Benge and Ewing both is that they don’t think too much about what they aren’t doing right. With another game, there isn’t a ton of time to dwell on the past. Benge plays like a big kid, just happy to be out at the ballpark doing what he loves. Ewing is a bit more cerebral, understanding that even big leaguers fail, so he shouldn’t be afraid of failure.

“That’s a part of my game that I take a lot of pride in, I’ve always had a very level head,” he said. “It’s failing so much that it’s impossible to avoid it. It’s understanding that there are going to be good days and bad days, and there are going to be good weeks and bad weeks. That’s just part of it.”