MILWAUKEE — The Mets still have everything at stake in the regular season and the Brewers nothing, but you wouldn’t have known it by Friday’s game.

About the most excited the Mets got was an irate Carlos Mendoza barking at plate umpire Ramon De Jesus before and after the manager was ejected for protesting a called third strike on Francisco Alvarez in the fourth inning.

The Mets were flat in all regards for a second straight game, and that was even before Alvarez grabbed for his lower back after sliding into third base in the seventh inning and had to depart.

The catcher, diagnosed with back spasms, needed teammates’ assistance to walk from the dugout to clubhouse.

A total disaster of a night for the Mets concluded with an 8-4 loss at American Family Field that left them tied with Atlanta for the NL’s second wildcard.

Arizona, also in the mix for a wildcard, played a later game in San Diego after beginning the day even with the Mets.

Francisco Lindor returned to the lineup after missing the previous eight games with lower back tightness and reached base three times — he was 2-for-4 with a walk — but the shortstop appeared unsteady at times and committed a throwing error that led to an unearned run.

The Brewers, locked into a No. 3 seed for the postseason, jumped on Sean Manaea from the start and kept adding runs.

In his worst start of the second half, Manaea lasted only 3 2/3 innings and surrendered six runs, one unearned, on seven hits and two walks with one strikeout.

The start was his shortest since Aug. 10 in Seattle, and the five earned runs allowed were his most since July 19 in Miami.