The Mets optioned Hartlieb to Triple-A Syracuse ahead of Sunday's game against the Dodgers, Justin Toscano of The Bergen Record reports.
Hartlieb's demotion cleared a spot on the 26-man active roster for infielder Javier Baez (back), who was reinstated from the injured list. The 27-year-old right-hander was up with the Mets for just two days and didn't make an appearance out of the bullpen.