"It's a bad pitch from the get-go," Phelps said. "I'm talking in the bullpen about maybe throwing a cutter in on his hands."
Instead, the right-hander threw an 80-mph knuckle curve that Loney deposited in the right-center gap.
For the second straight game, the Marlins didn't have an answer for Loney. In Friday's 6-2 loss, Loney hit the go-ahead two-run homer off lefty Mike Dunn in the seventh.
In two straight days, Loney did significant damage, both times pouncing on the first pitch. Off Dunn, it was a fastball down the middle. Against Phelps, it was as if he was sitting breaking ball.
"James is a guy who is pretty much swinging," Marlins manager Don Mattingly said.
Mattingly is no stranger with Loney, having managed him in their days together with the Dodgers.
"They're going to have a plan," Mattingly said. "They're pretty good at looking at what you do and what your pitchers do. They're going to be looking for any kind of tendencies that you have against a lefty or a righty, and they're going to try to pick them out."
Phelps has been so dominant in the eighth inning, posting a 1.76 ERA in his first 27 appearances before Saturday. The Marlins are unsure if Loney exploited a tendency.
"I don't know if he's sitting on that," Mattingly said. "It's hard to sit on anything with Dunner because he hasn't pitched that much. But Phelpsy, they're studying him."
The inning unraveled after Loney's hit on Saturday. Catcher J.T. Realmuto was charged with a passed ball that advanced Loney to third. He scored the tying run on Michael Conforto's single to center, a hit that snapped an 0-for-20 slide.
"It's a stupid pitch from the start," Phelps said regarding Loney. "It kind of set the tone for the rest of that inning."
So effective all season, Phelps had allowed just two runs in his last 11 2/3 innings over 11 games. In that span, he struck out 17 and walked just two.
But the Mets scratched out two runs to claim a 4-3 lead on pinch-hitter Matt Reynolds' pinch-hit, two-out single.
"I was just trying to throw a fastball down and away," Phelps said. "It stayed in the middle. He put a good swing on it."
Joe Frisaro has covered the Marlins for MLB.com since 2002. He writes a blog, called The Fish Pond. Follow him on Twitter @JoeFrisaro and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.