Mastrodonato: Red Sox have little choice but to keep playing Kyle Schwarber at first base 

Even after Kyle Schwarber’s error on a routine play at first base led to the Red Sox’ 5-4 loss to the Mariners on Monday night, there isn’t much Alex Cora can do about it.

Schwarber has to play. He was acquired July 29 for the Sox’ eighth-best prospect, Aldo Ramirez, and called “one of the most impactful hitters that changed hands this week” by chief baseball officer Chaim Bloom at the time.

He’s going to be in the lineup every day and hit.

And with J.D. Martinez’s back spasms almost surely preventing him from going to the outfield again soon, Schwarber better hang onto his glove for the remainder of the season.

The Sox are going to live and die with the roster they have at this point in the year, and on Monday night, they died with it.

“I mean, it was in the glove, squirted out and that was it,” Schwarber said of his mistake. “Frustrated. I wanted to make that play. It should have been a one-two-three inning and turned into a lot more.”

Of course, it wasn’t all Schwarber’s fault the Red Sox lost on Monday.

It was a groundball off the bat of Jake Bauers that bounced straight into Schwarber’s open glove, then bounced out to allow Bauers to reach safely with two outs in the seventh inning. The next batter singled, then Mitch Hanniger roped a hanging slider from Ryan Brasier over the left-field wall for a three-run homer that proved to be the difference.

Cora thought about keeping Eduardo Rodriguez in the game for the seventh inning, but Rodriguez was at 107 pitches, second-most he’s thrown in two years, and it was time to reach into the razor-thin bullpen. Brasier was the choice, despite not pitching all that well since coming up from Triple-A Worcester. He’s allowed a home run in back-to-back appearances.

So it’s not all the defense’s fault the Red Sox lost on Monday. But the defense sure has been an issue.

“We’ve been struggling defensively the whole season,” Cora said. “We have some good stretches that we play good defense, and when we do that, most of the time it seems like we’re winning games. That’s the bottom line. At this level, you have to be good defensively. I know we’ve got X amount of games, and we just have to keep working with them. It’s not that we hope we will get better. We know we can be better. We just have to make plays.”

The Sox have been making errors left and right. Unearned runs are their middle name. Bobby Dalbec’s 11 errors at first base are second-most among big league first baseman this year. Rafael Devers’ 20 errors at third base are five more than any other third baseman. And as much credit as Hunter Renfroe has gotten for his throwing arm, his 10 errors in right field are five more than any other right fielder.

Renfroe also shared some blame on Monday, as he over-ran a line drive single in the second inning and let it bounce off him, allowing the Mariners to move a runner to third base. The runner scored the very next play on a ground out.

What can Cora do about it? Not much.

If Schwarber isn’t playing first base, where is he going to play? Martinez is the DH. Alex Verdugo is in left field against right-handed pitching, and the Sox have seen enough of Verdugo in center field lately to prioritize Kiké Hernandez getting the starts in center. That leaves one position for Schwarber: first base.

It’s not that he’s been awful there. It was just his fourth big league start at first base and his first error. He also handled a double play ball well earlier in the game, and he looks natural stretching off the bag. With time, he might handle the position OK.

Unfortunately, he doesn’t have much time, as the Sox are in the midst of a playoff race in which every game matters.

“I’m not really concerned about it,” he said. “I knew the day was going to come that I was going to make an error. It’s inevitable to happen. It’s unfortunate that it turns out to be the thing that kind of turns the tide and makes it sting a whole lot more.

“I’ve learned a new position in the big leagues before in left field. I’ve DH’d plenty of times in my career in interleague. There’s no excuses. There’s no excuse. Just have to be able to keep rolling and have the short memory and be ready for tomorrow.”

Bobby Dalbec will be at first against lefties, pushing Schwarber to left field. Dalbec is hot and deserves to play, too, but over who? Schwarber’s bat has cooled off lately, but he’s too good to be on the bench. The Sox need his infectious plate approach and he fits nicely in the two-spot in the order.

There’s really no other choice unless the Sox want to bench Verdugo altogether or bench Martinez, but neither one of those choices make a lot of sense either.

So, defense will suffer. It has suffered all year. It cost the Red Sox another game on Monday.

“It’s frustrating, but we just gotta keep working at it,” Cora said. “We have to keep putting in the work and hopefully we get on a hot streak defensively so that we play clean baseball. When we do that, we’re really good.

“But like I always said, you give the opposition more than 27 outs, most of the time they’re going to take advantage. And it seems like right now, whenever we open up the window for them or the door — whatever you want to call it — they take advantage and we pay the price. We just gotta keep going.”