This time, Flexen allowed five earned runs on eight hits and one walk, striking out two.
Flexen said he's had blisters before, but he thinks he should be able to make his next start.
"It's just kind of a freak thing, it just pinches against the nail," Flexen said, adding that the blister didn't affect his command, and he "didn't even feel it come off."
Manager Terry Collins said the Mets were already planning on removing Flexen after the third.
"The third inning, he went out, and I guess the blister was formed in the second inning," Collins said. "In the third, [pitching coach Dan Warthen] came in and told me he had it right when we were getting ready to take him out."
The Mets trailed, 5-0, when Flexen left. Reliever Chasen Bradford came in for Flexen in a double switch, with Jose Reyes taking Neil Walker's spot at second base.
Max Gelman is a reporter for MLB.com based in Denver and covered the Mets on Wednesday. This story was not subject to the approval of Major League Baseball or its clubs.