It all added up to a 9-1 rout on Thursday night that snapped the Mets' modest two-game winning streak.
Garza allowed two hits over eight innings to rebound from a horrendous outing and Ryan Braun hit one of three homers for the Brewers.
"We are not swinging the bats very well right now," said Mets manager Terry Collins, whose team has scored just 10 runs in six games.
Gee (4-3) didn't give his team much of a chance. The Brewers took a 6-0 lead after three innings and cruised to their fourth consecutive win.
"There is no excuses," said Gee, who was making his third start after missing two months with a strained right lat. "The layoff is not an excuse for me. It is not that perplexing, either, because I haven't felt good. The ball is just not coming out right the last couple of starts."
Granderson, who missed two games because of flu-like symptoms, is mired in a .189 slump (7-for-37). Murphy is in a .170 (7-for-41) skid.
"The keys to your lineup have to continue to do it," Collins said. "When they get in a funk, someone else has to step up, and we are not doing that yet. It has been tough."
Garza (7-7) gave up five runs in just one-third of an inning Saturday at Washington, the shortest start of his career.
It was a different story against the Mets. The right-hander yielded a third-inning single to Wilmer Flores, recalled from Triple-A Las Vegas earlier in the day, and a seventh-inning homer to Lucas Duda. Garza struck out four and walked one.
"His last start probably upset him enough that he had a lot to prove tonight, and he threw the ball well," Collins said.
Milwaukee limped into the All-Star break, losing 11 of 13 games. They have won five of seven since then to open a three-game lead over the St. Louis Cardinals and Pittsburgh Pirates in the NL Central.
During their slump, the Brewers hit only seven homers in 13 games. Since the break, they have 12 in seven games.
Lucroy hit his 12th, and Davis added 17th homer, both solo shots. Braun had a two-run shot, deep to left field. It was his 14th long ball and extended his hitting streak to 12 games.
"Hitting is contagious," Davis said. "Once we start popping them out of the yard it feels like everybody is going to start."
Duda's homer was his 16th, a career high.
Gee lasted only five innings for the second consecutive start and allowed six runs, the most he has given up all season. The right-hander allowed six hits and two walks and struck out six.
It was the most runs given up by Gee since he allowed seven in an 8-3 loss at Philadelphia on April 9, 2013, a span of 40 starts.
He was replaced to open the sixth by Daisuke Matsuzaka, whose first pitch was hit by Davis over the fence.
NOTES: The Mets optioned OF Kirk Nieuwenhuis to Las Vegas. ... Mets SS Ruben Tejada was given the day off as a precaution after being hit in the helmet by a pitch from Seattle's Taijuan Walker on Wednesday.