Tempers were calm a day after Pablo Lopez was ejected for hitting Ronald Acuna Jr. on his first pitch of the game. The Marlins got a big assist from Alcantara, who saved the bullpen from extra work a day after Miami had to use five relievers to cover nine innings.
''It starts with Sandy,'' Marlins manager Don Mattingly said. ''He threw some pitches early, but to get through six was huge for us. Obviously our 'pen was a little bit out of gas.''
Alcantara (5-7) walked the first two batters he faced and issued two free passes in the third, but didn't allow a hit until Ozzie Albies singled with two outs in the third. He gave up one unearned run and five hits with four walks and four strikeouts, improving to 2-0 with a 2.68 ERA in six career starts against Atlanta.
Alcantara's fastball hovered at 100 mph throughout his stay on the mound.
''I was mad today because something happened last night with Lopez,'' Alcantara said. ''I was just going to attack them. We know they are a really aggressive team, and I've got to use my fastball. I came from the bullpen with velo and you guys saw it.''
Yimi Garcia earned his 13th save in 16 chances after facing four batters in the ninth. He got pinch-hitter Pablo Sandoval to pop up and Acuna to strike out before Freddie Freeman singled. Albies lined out to end it.
The Marlins led 2-0 in the third. Jon Berti singled, advanced on a sacrifice bunt and scored on Jazz Chisholm Jr.'s single to right. Chisholm moved up on Starling Marte's walk and scored on Cooper's single.
Cooper began the sixth with his seventh homer, taking rookie starter Kyle Muller deep into the right-field seats, making it 3-1.
''I was trying to ambush him, honestly,'' Cooper said. ''I was looking for a first-pitch fastball. ... I just put a good swing on it and thankfully it went out here. I don't know if would've gone out in Miami, though.''
Atlanta trimmed the lead to 2-1 in the fifth. Acuna reached on a fielding error by third baseman Berti, advanced to third on Freeman's single and scored on a single by Albies, the NL leader with 59 RBIs.
The Braves, who managed just two hits in Friday's 1-0 win, scratched out a run in the seventh to pull within 3-2. A two-base fielding error by Miami left fielder Jesus Sanchez allowed pinch-hitter Ehire Adrianza to reach. Adrianza advanced on a wild pitch by Dylan Floro and scored on Freeman's single. Floro stranded two runners to escape further trouble.
Muller (1-2), facing the Marlins for the first time, gave up four hits and three runs with four walks and seven strikeouts in 5 2/3 innings.
''He never gave in,'' Braves manager Brian Snitker said. ''I love the way he competed. That was very impressive I think for a young guy ... he got a little adversity and he hung in there and kept the game in check.''
The three-time defending NL East champion Braves, at 40-42, were trying to reach .500 for the first time since June 8 and the sixth time this season. Atlanta, which had won 10 of 16, has yet to top .500 this season.
Miami, last in the division, had dropped three of four.
Because he threw only one pitch on Friday, Lopez is in line to start early next week against the Los Angeles Dodgers. Manager Don Mattingly wasn't sure which day Lopez will go.
According to the Elias Sports Bureau, Lopez became the first pitcher to throw one pitch and take a loss since Baltimore's Art Schallok did so on Aug. 3, 1955, against the Kansas City Athletics.
Miami acquired RHP David Hess in a deal with Tampa Bay, which received RHP Justin Sterner and cash considerations. Jordan Holloway was optioned to Triple-A Jacksonville.
Veteran RHP Charlie Morton (7-3, 3.74 ERA) faces Miami RHP Zach Thompson (2-2, 1.50) in Sunday's series finale. The 37-year-old Morton is 0-1 with an 8.20 ERA in two starts against the Marlins this year. Thompson will face the Braves for the second time in his career. He beat Atlanta with five scoreless innings on June 12.
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