"I wanted to get around 90 pitches," Haren said. "I was feeling it at the end. I'm sure I'll be a little sore. The spring has been pretty smooth for me until that last inning."
Before the regular season begins on April 6 against the Braves at Marlins Park, Haren has one more start, which will be on Saturday in exhibition against Double-A Jacksonville.
The Marlins have not announced their rotation past Henderson Alvarez going on Opening Day. But the rest of the starting five is shaping up to be Mat Latos going in second game, followed by Tom Koehler, Haren and Jarred Cosart, who is being pushed to the back of the rotation as he recovers from a blister on his right middle finger.
The fact Haren has made at least 30 starts in 10 straight seasons is a reason the Marlins aren't concerned about Spring Training performances.
"This guy has been around a long time," manager Mike Redmond said. "He knows how to pitch. He's taken the ball all the time. He's been through the ringer. He knows what to expect, how to prepare.
"Look for him, when the lights turn on, to give us a chance to win, for sure."
Haren cruised early against the Mets. He threw three perfect innings to start the game, and retired his first 11 before David Wright's two-out single in the fourth. Lucas Duda followed with a two-run homer to put New York on the board.
Then Mets broke the game open in the sixth, with Duda delivering a three-run double and Michael Cuddyer connecting on a two-run homer.
Haren entered Monday with a 1.93 Grapefruit League ERA, but he finished at 4.66 in 19 1/3 innings.
"Nothing is easy for me. It's never easy," Haren said. "I was pretty successful until that last inning. I was just one or two pitches away from getting out of it. I couldn't make the pitches at the right times. It's tough to get up there about 90 pitches and get into a jam, especially at this point of Spring Training. It's tough, especially going through the middle of their lineup."
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.