Tyler Samaniego laments cutter launched by Phillies slugger Kyle Schwarber to beat the Red Sox

Tyler Samaniego had plans for the 3-and-1 cutter he threw to Kyle Schwarber in the eighth inning of the Red Sox’s 3-1 loss to the Phillies on Thursday night.

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“Just trying to get the cutter away,” he said. “Get some soft contact, maybe a double play.”

The cutter had other ideas.

“Just backed up on me,” he said. “Right in his nitro zone, which is not ideal.”

Between Schwarber’s status as one of the best sluggers to ever dig in at Fenway Park and the recent tear he’s been on, making a mistake was a dangerous proposition — even for a pitcher who had been throwing as well as Samaniego.

Schwarber shipped it into the stands beyond the Phillies bullpen in right field for a two-run homer that all but decided what had been a scoreless. It was his National League-leading 18th homer of the season, his second in three nights at Fenway and his sixth in his past seven games.

Even Phillies interim manager Don Mattingly felt some sympathy for Samaniego, who hadn’t allowed a run over 15 innings of work up to that point.

“He’s been really good all year until that inning,” Mattingly said. “So to get to him there was huge.”

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Schwarber faced Samaniego in the series opener (working a walk) and took the mental notes into Thursday’s at-bat.

“I’m trying to stay in the strike zone,” Schwarber said. “I know he has a sinker; I know he has a cutter. It’s more about trying to stay in the zone and get him up. It’s not like I’m looking for a certain pitch or a certain thing to do.”

Schwarber owns a .333/.464/.667 slash line at Fenway, and his 1.131 OPS is the fifth-highest of all time by a player with at least 100 plate appearances. The only players higher are Frank Robinson (1.188), Johnny Grubb (1.179), Ted Williams (1.148), and Brandon Lowe (1.138).

“He’s a great hitter,” Samaniego said. “Obviously, there’s a challenge every time he steps up to the plate if you don’t execute your pitches, which I didn’t. And he makes you pay for your mistakes.”

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Peter Abraham and Alex Speier of the Globe staff contributed.