The loss left Milwaukee a half-game behind Philadelphia for the final NL wild-card berth. The Phillies lost their fifth straight, 2-0 to the Cubs in Chicago.
''We still have an opportunity in front of us and got to come out and play a good game tomorrow,'' Milwaukee manager Craig Counsell said.
The Brewers have six games remaining over the next six days, all at home - three more against Miami and three against Arizona. The Phillies have seven games to go, all on the road. They play four games at Washington, starting with a doubleheader Friday, then three at Houston.
Garcia's 411-foot blast came off Freddy Peralta (4-4), a regular starter making his first relief appearance of the season.
Garcia, who was with the Brewers in 2020 and 2021, was put on the injured list Sept. 13 with a left hamstring strain. He was sent to Triple-A Jacksonville for a rehab assignment Monday before being activated Thursday.
Milwaukee was leading 2-0 when Peralta came on in the seventh inning and retired the side in order. In the eighth, he gave up two singles and a walk, loading the bases before Garcia unloaded on a 1-2 pitch, a 95 mph fastball.
''By the feel, by the sound, I know this ballpark really well,'' Garcia said. ''I know the ball runs very well here and I knew it by the way I hit it.''
Peralta, who has started 16 games, made his last start Sept. 25, when he was activated from the 15-day injured list and pitched two innings. He had been suffering from right shoulder inflammation.
''I was ready for it, the situation that I was going to pitch, but it didn't work for me today,'' Peralta said.
Counsell said ''it's a tough spot, for sure, but I'll give Freddy the ball any time, I don't care what the situation is.''
Milwaukee starter Eric Lauer pitched five shutout innings, striking out nine and giving up one hit and no walks while throwing 71 pitches. The left-hander had pitched 2 2/3 innings in his previous start, on Sept. 23, after returning from the injured list with left elbow inflammation.
''We never count ourselves out, so if we can control what we can control and we can win some baseball games, things will work out for us,'' Lauer said.
Milwaukee took a 2-0 lead in the second inning off lefty starter Braxton Garrett. Christian Yelich singled and scored when Mike Brousseau singled and Garcia committed a throwing error from right field. Two batters later, Brosseau scored when Keston Hiura doubled to right.
Milwaukee lost a potential run when Hiura tried to steal third base and was thrown out by catcher Nick Fortes. The next batter, Victor Caratini, singled to centerfield.
In the sixth inning, Marlins right-hander Jeff Brigham lifted a leg and shook his arms in celebration when, after giving up two doubles and a walk to load the bases, he got Caratini to hit into an inning-ending double play.
''I thought we had good at-bats, it just didn't work for us, unfortunately, at the right time,'' Counsell said.
A total of five pitchers came on in relief of Garrett. Tommy Nance (1-3), who was activated from the injured list Thursday following a groin injury, pitched the seventh inning for the win. Dylan Floro worked the ninth for his ninth save.
The Marlins' 5-4 loss to the Mets in 10 innings Wednesday was their fifth straight loss in extra-inning games. It was also their 11th walk-off loss of the season, tied with the Yankees for most in the majors.
KINGS OF K'S
Milwaukee pitchers rank third in the NL in strikeouts (1,468). They struck out 14 Marlins batters Thursday.
The Marlins have the fourth-lowest winning percentage (.417) in the NL, but some of its players are posting high marks. Jon Berti leads the majors in stolen bases. He stole his 38th base on the first pitch after he singled off Peter Strzelecki in the sixth inning. . Entering Thursday, in 18 games since being recalled from Triple-A Jacksonville, OF Bryan De La Cruz was batting .421 with five home runs and 17 RBI. His 1.278 OPS was third among qualifiers in the majors in that span. He went 0 for 3 on Thursday.
Marlins: Bryan Hoeing took over for Garrett to start the fifth inning but left after the second batter he faced, Willy Adames hit a ground ball that struck Hoeing in the left calf. Hoeing said the leg didn't feel stable enough for him to continue pitching. ... 1B Garrett Cooper (pinky fracture) and LHP Steven Okert (left triceps tightness) were put on the IL. . Jesus Sanchez was recalled from Triple A-Jacksonville. . OF Jerar Encarnacion and OF Luke Williams were optioned to Jacksonville.
The second game pits Marlins RHP Sandy Alcantara (14-8, 2.32 ERA) against Brewers RHP Corbin Burnes (11-8, 3.11 ERA) on Friday. Alcantara leads the majors in complete games (five) and innings pitched (220 2/3). Burnes, the reigning NL Cy Young Award winner, is second in the NL in strikeouts (231).
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