The Marlins' top prospect slugged two homers and knocked in a career-high seven runs as the Class A Advanced Hammerheads routed the St. Lucie Mets, 11-4.
Overall, Yelich went 4-for-5 with two runs scored as he raised his average 14 points to .290. His previous career high for RBIs came on April 18 last year, when he went deep and plated four.
"I just got some good pitches to hit and didn't really miss them," Yelich said.
The 20-year-old outfielder got on base in his first four plate appearances, starting with a single in the first inning. In an 0-2 hole in the third, he battled back to hit a grand slam off Chase Huntington, tying the game at 4-4.
"I think he threw a 3-2 slider," Yelich said. "I just barreled that pretty good and it ended up going over the fence."
After an RBI single, Yelich capped his day with a two-run shot off reliever Kyle Allen in the sixth.
"I got into a good hitter's count, it was 3-1, I think," Yelich said. "He threw a fastball and I hit it well again."
On the whole, eight players in the Hammerheads lineup recorded base knocks as the team totaled 14 hits on the night. Jacob Realmuto also went deep twice, driving in three.
"We always give each other a hard time, we actually live together," Yelich said of Realmuto. "It was a pretty good night for our house. I was happy for him, he was putting good swings on balls. I wasn't trying to match him or anything, but I'll definitely take it."
No. 3 Marlins prospect Jose Fernandez (1-0) won his debut with Jupiter after giving up four runs on five hits over five frames. He had been one of the best starters in the Class A South Atlantic League, leading pitchers with a 1.59 ERA, 0.87 WHIP and 99 strikeouts in 79 innings before his promotion.
"He's got great stuff," Yelich said. "I thought it was a pretty good start. They didn't really hit any balls hard against him, just some balls falling in. He kept us in the whole time. We put up the six runs [in the third] and he shut the door the next two innings. He's a gamer and a fun guy to pay with."
In 50 games this season, Yelich has collected nine homers and 28 RBIs to go along with a .914 OPS. The 23rd overall pick in the 2010 Draft has been honored as a Florida State League All-Star and will be playing the in the All-Star Futures Game on July 8 in Kansas City.
"It's awesome," Yelich said. "I grew up watching the Futures Game ever since I can remember and always wanted to play in it. To finally get the the opportunity is pretty special, I'm looking forward to it."