The left-handed-hitting left fielder is batting .318 with two homers and seven RBIs in 24 games in September after going 0-for-3 with a walk in Wednesday's 3-2 win over the Phillies, when he hit third. He's also showing plate discipline, posting a .408 on-base and .443 slugging percentage in the month.
For the season, the rookie is batting .282, and he's getting steady playing time against lefties and righties alike.
"We've talked about the frontline players, the guys who play every day," manager Mike Redmond said. "They play whether it's right-handers or left-handers out there. It doesn't matter. I think his at-bats have been great. He's faced a lot of tough lefties."
Yelich's overall splits aren't great against lefties. For the season, he's is batting at a .167 clip against southpaws -- after taking on Philly left-hander Cole Hamels and reliever Cesar Jimenez on Wednesday -- compared to .354 against righties.
"I think it's so important for him to keep going out there and getting these at-bats, especially against left-handed pitchers," Redmond said. "That experience is big. You're not going to hit lefties if you don't play against them."
Yelich opened the season in the Minor Leagues and was Miami's second-ranked prospect, according to MLB.com, behind Jose Fernandez, before rocketing his way to the Majors.
The Marlins have gone through their growing pains. Yelich, too, is learning. He batted .216 in nine games in July and .275 in 27 games in August.
"You can kind of learn from it," Yelich said. "It's still not a lost year. There are some guys in here who have gotten some experience, and kind of learned what it's like to play in the big leagues. You can take that into the offseason and kind of build on it."
Joe Frisaro is a reporter for MLB.com. He writes a blog, called The Fish Pond. Follow him on Twitter