The Cubs were the only team in the majors that hadn't dropped back-to-back games before two straight losses to Milwaukee at Wrigley Field. Chicago had won three of four and 12 of 15.
"It's encouraging," Brewers star Ryan Braun said of the team's consecutive comeback victories. "I think the last few years that's kind of been a staple for us, something we've been able to do, just steal some wins late in games, continue to compete, continue to believe that we're going to come back."
"I've been swinging too hard. I just try to focus, swing at strikes and put a good swing on it," said Garcia, noting he's had to make adjustments to the NL after playing for Tampa Bay last season.
Luis Urias reached on an infield single for an additional run.
David Phelps (2-1) threw a scoreless inning for the victory.
Urias had three hits and Braun and Garcia added two hits apiece for the Brewers, who beat Chicago 4-3 on Friday night.
Anthony Rizzo homered and had three hits and Happ added two doubles for Chicago.
"It's tough. The last few years, they've done a really good job," Rizzo said of the Brewers. "I think that starts with Craig Counsell and the way he's managed a lot of moving parts there with their team. They're always competing. They're a really good team."
Braun doubled, advanced on Casey Sadler's wild pitch and scored the go-ahead run on second baseman Jason Kipnis' fielding error in the sixth. Braun doubled twice after he was 0 for 8 entering the game since he returned from the IL on Tuesday from an infected right index finger.
"I'm always anxious to get back in the lineup, especially when we're scuffling offensively," Braun said. "It's just a matter of trying to find my timing and rhythm and start to get a little bit better with my pitch recognition. Today was the first game all year where I felt like my approach was in a good place."
Right-hander Adrian Houser retired his final eight batters after allowing three runs in the first two innings. He struck out five and gave up five hits.
Rizzo hit a first-pitch solo shot to the left-field basket off Houser in the first. After back-to-back walks, Happ doubled to extend the Cubs' lead to 2-0.
Rizzo doubled to center for a 3-0 Cubs lead in the second.
Right-hander Colin Rea allowed three runs and four hits in 3 1/3 innings in his first start for the Cubs since 2016. He filled in for Alec Mills, who started Friday in place of Tyler Chatwood (mid-back tightness).
Saturday's start was shifted to 2:20 p.m. from 7:15 p.m. because of forecasted inclement weather.
Cubs: Chatwood (mid-back tightness) will start during Monday's doubleheader against St. Louis after missing his start Friday. . 3B Kris Bryant (sore left wrist and finger) returned to the lineup after missing two straight games. He batted leadoff and went 1 for 5. . LHP Brad Wieck (left knee soreness) has had a setback in his return from a hamstring injury, manager David Ross said. . RHP James Norwood (right shoulder) is progressing with his throwing program, Ross said.
Brewers RHP Josh Lindblom (1-0, 5.68 ERA) starts Sunday's series finale against the Cubs and LHP Jon Lester (2-0, 1.06 ERA). Lindblom earned his first victory as a Brewer and starter Aug. 6 against the Chicago White Sox. Lester allowed a run and three hits in six innings against Cleveland in his last start.
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