CHICAGO — Unlike the Mets, the Cubs are still playing for something, finding themselves locked in a dogfight as they try to fend off the charging Cardinals and Brewers in what has become a hectic race for the NL Central.

It’s why Mets manager Terry Collins figured right hander Robert Gsellman would be in for “a big challenge” Tuesday night against the Cubs.

But that challenge proved too rigorous for Gsellman, who lasted just four innings in the Mets’ 8-3 loss. He allowed five hits and a career-high five walks, his ERA rising to 5.58.

“All those walks are going to lead to runs eventually,” Gsellman (6-7) said.

Kris Bryant delivered the biggest blow, a three-run shot in a four-run fourth. But the deluge began with a perfectly executed safety squeeze bunt from pitcher Jose Quintana.

Schedule released

The Mets will open the 2018 season by hosting the Cardinals on March 29. Meanwhile, the Subway Series will be split into a pair of three-game series and the Mets will take on the AL East in interleague play, meaning a visit to Fenway Park for the first time since 2009.

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Extra bases

Adam Fisher, the longest-tenured member of the Mets’ front office, has been hired away by the Braves to serve as assistant general manager. Fisher was the director of baseball operations and had been with the Mets since 2004 . . . Reliever Erik Goeddel was sent to New York for tests after dizziness and blurred vision the last few days . . . Noah Syndergaard was expected to play catch yesterday as he works to rejoin the Mets before the end of the season . . . As expected, the Mets added a third catcher to the roster, Tomas Nido, who hit .232 for Double-A Binghamton.