The Mets optioned Hartlieb to Triple-A Syracuse on Wednesday, Deesha Thosar of the New York Daily News reports.
Hartlieb's demotion clears a spot on the active roster for a fresh bullpen arm in right-hander Nick Tropeano, who was recalled from Triple-A in a corresponding move. After the Mets claimed him off waivers from the Pirates on July 8, Hartlieb was called up to the big club a couple days later and made four relief appearances. He gave up two earned runs on three hits and three walks over four innings.