Freeman led off the 10th inning with a home run into the right-field seats , lifting the Atlanta Braves to a 4-3 win over the Milwaukee Brewers on Saturday night.
The Braves recovered to win their fourth straight game after Luke Jackson blew a 3-2 lead in the ninth.
Freeman pulled a fastball from Josh Hader (0-3) for his 10th homer.
Braves manager Brian Snitker called the matchup "two of the best left-handers in the game right there, going one-on-one."
The tough matchup didn't alter Freeman's approach. Asked what he was looking for, Freeman said: "A strike, the same with anybody on the mound. Just looking for a pitch to hit."
Jacob Webb (2-0) pitched a perfect 10th for Atlanta.
Riley, the Braves' rookie left fielder still in his first week in the majors, hit a go-ahead, two-run homer in the sixth for a 3-2 lead.
"For what he's doing the first four games, it's hard to put in words," Freeman said. "... He's aggressive. He's aggressive in the zone. He's taking pitches out of the zone, which is very hard for a young guy. I'm just very impressed with how he has approached his first four games."
Riley joined the on-field celebration when his new teammates surrounded Freeman following the game-winning homer, drenching the first baseman with a cooler.
"For Freddie to hit a walk-off was super cool," Riley said. "I've never been a part of anything like that."
Riley's homer off left-hander Alex Claudio gave him eight hits, including two homers, in four games since he was called up from Triple-A Gwinnett. The eight hits are an Atlanta record for a player's first four games.
Riley singled in the second but made a rookie mistake when he was fooled by shortstop Hernan Perez, who pretended to field a throw at second on Brian McCann's fly ball to fight field. Riley slid head-first into second before standing to watch right fielder Christian Yelich throw to first base to complete the double play.
The front of Riley's shirt was still covered in dirt when he made up for his mistake with the homer.
The Brewers left the bases loaded in the third and ninth and left 10 runners on base overall.
"We didn't capitalize enough on our offensive opportunities," Brewers manager Craig Counsell said, adding the missed chances "cost us in the end."
Jackson hit Keston Hiura with a pitch to open the ninth. Hiura moved to third on Orlando Arcia's one-out single to right and scored on Lorenzo Cain's high bouncer over third baseman Josh Donaldson for a 3-3 tie.
Braves right-hander Kevin Gausman allowed two runs in six innings.
Brewers: Counsell says a decision must be made on RHP Jimmy Nelson (right shoulder) and his possible place on the staff following one more rehab assignment with Triple-A San Antonio on Thursday. Nelson gave up three hits in 5 1/3 scoreless innings Friday night.
Braves: Donaldson likely will be given a rest Sunday. Snitker said he plans to give Riley his first start at third base. Riley made his fourth straight start in left field after pregame fielding drills at third base, his primary position in the minors.
Milwaukee right-hander Chase Anderson came off the injured list to allow one unearned run on two hits with four walks in four innings in his first start of May. He was placed on the injured list on May 1 due to a blister on his right middle finger.
The Braves released left-hander Jonny Venters, whose comeback from his third Tommy John surgery helped him win the NL Comeback Player of the Year Award last year. Venters, 34, had a 17.36 ERA in nine appearances. The Braves recalled left-hander Jerry Blevins only four days after he was designated for assignment. The Brewers optioned right-hander Jacob Barnes to Triple-A San Antonio.
Yelich threw out Markakis at the plate to end the eighth. Markakis was trying to score from second on Ozzie Albies' single.
Brewers: RHP Brandon Woodruff (6-1, 3.72) will make his first career appearance against Atlanta in Sunday's final game of the three-game series. He has won his last four starts and is 5-0 over his last six starts.
Braves: RHP Mike Foltynewicz (0-3, 8.02) is 2-2 with a 2.90 ERA in six career games, including five starts, against the Brewers.
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