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The boos showered upon Reed Garrett as he trudged off the field with his head bowed after surrendering a grand slam, the righty the face of fans’ ire though far from the only target.

Fans might not have been thrilled with Clay Holmes, either, who took down just 5 ⅓ innings on the front end of a doubleheader that would again test the Mets’ staff depth. And they were not happy with manager Carlos Mendoza, who elected to pull Holmes after 90 pitches from a game the club was leading.

The decision backfired, and what looked like an encouraging afternoon gave way to one more low point during a sixth-inning implosion. The location has changed but the free fall has not, the Mets opening a homestand by dropping a fourth straight game and a 14th in their past 17, beginning a long day Wednesday with a 7-2 loss to the Brewers at a Citi Field in which empty seats outnumbered fans.

Since the June 13 start of this plummet, the Mets entered play with the worst ERA in baseball and the fourth-worst OPS, simply doing nothing right.

Their offense responded by playing adequate small ball to manufacture two early runs and grab a lead, but then went silent. Their pitching, meanwhile, gifted the lead right back in a five-run sixth inning in which blame could be spread around.

Up 2-1, Holmes walked Christian Yelich and induced a fly out from Jackson Chourio before Mendoza walked to the mound and lifted the big righty after 5 ⅓ effective, if wild (four walks) innings in which he had allowed one run up to that point.

In his first season since being converted from a reliever, Holmes already has set his season-high for innings — but also was pitching on six days’ rest for a rotation that has four starting pitchers on the injured list and on a day when the team needed to cover 18 frames.

Mendoza’s aggressive decision to call for Garrett, his fireman, in the sixth inning blew up. With his first two pitches, Garrett allowed a game-tying double to Brice Turang and a smacked single to Isaac Collins. After losing the lead, Garrett lost the strike zone in walking Jake Bauers and falling behind 3-0 on Joey Ortiz.

Ortiz, a light-hitting infielder, then pulled a 3-1 cutter into the left-field seats for a grand slam that put the Brewers ahead by four runs — or the entirety of the Mets’ offense during the previous three-game sweep in Pittsburgh.

Wednesday, the Mets’ offense tallied just two hits against Freddie Peralta and the Brewers’ bullpen, at least efficient with their knocks.

They used a nifty hit-and-run, with Jeff McNeil taking off for second base and Luis Torrens poking a single into right to create a chance in the third inning before Brett Baty lofted a sacrifice fly.

In the fourth, Juan Soto walked, stole second and scored on a single from Pete Alonso.

But the Mets went 0-for-18 the rest of the way, held off base apart from Alonso getting plunked in the sixth.