Daniel Murphy's three-run homer off closer Steve Cishek rallied New York to a 3-1 victory, but it didn't erase the progress Cosart is making.
Complementing his mid-90s fastball with an improving changeup and breaking ball, Cosart is throwing like a top-of-the-rotation pitcher.
"My fastball is my bread and butter," Cosart said. "Being able to throw [offspeed] pitches for strikes and change eye levels and change speeds to get them off my best pitch has been huge."
An example of how effective Cosart's secondary pitches were was reflected in the third inning. Facing left-handed-hitting Lucas Duda, Cosart got a swinging strike on a 2-1 changeup. With the count even, his next pitch was a sinker that Duda weakly tapped to the mound for an easy out.
Cosart needed to be on his game to match Dillon Gee, who gave up one run in 7 2/3 innings. The game ended in a brisk one hour, 58 minutes.
"That's what happens when you throw strikes," Cosart said. "You establish early. The other team knows they have to swing. I started executing pitches after the third inning, and he obviously was doing the same thing."
Cosart followed up a strong start in Philadelphia, in which he allowed just one run in six innings and earned his first victory of the year.
Losing in heartbreaking fashion is part of the game.
"It's baseball," Cosart said. "All our job is as a starter is to go out there and try to keep us in the game. I was able to do that. I didn't start off as well as I'd like to. I got behind some hitters.
"I got into a pretty good groove there in the third. Any time you lose, it's tough."
Joe Frisaro is a reporter for MLB.com. He writes a blog, called The Fish Pond. Follow him on Twitter @JoeFrisaro. This story was not subject to the approval of Major League Baseball or its clubs.