CHICAGO — As somebody present for their last great collapse who still watches plenty of Mets games, Billy Wagner understands what’s at stake over this final week of the regular season.

“I know how difficult it is playing in New York, especially at this moment,” the Hall of Fame closer told The Post on Tuesday in a phone conversation.

The Mets began the day tied with Cincinnati for the NL’s third and final wild-card spot, but the Reds owned the tiebreaker based on winning the season series.

Don’t miss Mike Puma’s text messages from Queens and beyond — he’s giving Sports+ subscribers the inside buzz on the Mets.

It’s a Mets team that held a five-game lead in the wild-card race on Labor Day weekend, but has sputtered down the stretch. In a larger sample size, the Mets were 35-52 since June 13 as play began.