"Today was tough," Koehler said. "I didn't give the team a chance to win. Normally I don't care how many runs I give up, as long as I give the guys an opportunity to win the game.
"That wasn't the case today. I gave up the big homer in the second inning [to Michael Conforto] and then three doubles in the fourth or fifth to score a bunch more runs. You can't really get much going offensively when you're playing from behind like that."
Koehler (8-8) had his ERA rise from 3.38 to 3.71 after Miami lost the series opener.
The tone was set in the second inning when Conforto belted a three-run homer on a 3-1 pitch.
More damage came in a four-run fifth inning that blew the game wide open. On a 3-1 pitch, Yoenis Cespedes blistered a two-run double to right-center that nearly cleared the wall for a home run. Two batters later, Wilmer Flores ripped an RBI double and Koehler had his shortest outing in 10 starts, or dating back to the 3 1/3 innings he threw at Citi Field in a no-decision against the Mets on May 30.
"When you fall behind -- no matter who you're facing -- you're forced to throw fastballs in better parts of the plate than you normally want to," Koehler said. "They did a good job when I was behind in the count and had to come back with a fastball. They didn't miss it or foul it off. They hit them hard.
"Anytime you give up a bunch of extra-base hits, it's going to keep guys in motion and keep guys scoring. Unfortunately, I pitched from behind the entire day and couldn't get a good rhythm."
In three starts against the Mets, Koehler has allowed 19 runs (18 earned) on 19 hits in 11 innings. His ERA is 14.73 against New York, and 2.26 in his other 18 outings.
"Just missed location tonight," manager Dan Jennings said. "Not a lot you can say about this game. It was ugly. Maybe the ugliest game we've played all year. Missed location by T.K. It's certainly not indicative of what he's done this year. Just a bad game. Unfortunately, you're going to have some of those."