Conlon made his debut for the Mets against the Cincinnati Reds on May 7, 2018, with an Irish tricolour stitched into his glove. He started off well, retiring seven of the first eight Cincinnati batters, but gave up a solo home run to Billy Hamilton in the third inning and two more runs in the fourth before being taken out of the game. In total, Conlon pitched 3.2 innings, allowed three runs on four hits and two walks, and struck out one. He also recorded his first major league hit on a single up the middle, but jammed his thumb while swinging the bat, which is one reason he was pulled early.
