"You can't let the situation get the best of you," Yelich said. "Get a good pitch to hit and put a good swing on it. I ended up hitting it pretty hard and hit a home run. It's pretty cool."
Yelich, who was Miami's first-round pick in the 2010 First-Year Player Draft, has not played above Class A ball. The 21-year-old is expected to open the season at Double-A Jacksonville, but he is giving the organization something to think about in terms of making the Opening Day roster.
"He's playing relaxed, he's having fun," manager Mike Redmond said. "We feel like in any situation he comes up, he has a chance to do something. He hits a homer to dead-center [field] to win it.
"That's a tough conversation. Like I said, I'm sure we will have to talk about it. We want to make sure we do what's best for him and the organization. I think we've all seen guys who have had great springs and struggle out of the chute, too. We've all seen that. I'm happy for him with the way he's playing at the way he's swinging the bat."
Jackie Bradley Jr., who is ranked Boston's No. 2 prospect by MLB.com, had a home run and an RBI double. Mike Carp added a solo homer in the fourth and Will Middlebrooks connected on a two-run shot in the seventh.
Miami pushed across a run in the first inning, but Jon Lester settled down nicely and finished with an impressive five-inning, one-run outing with four strikeouts.
After issuing a one-out double to Casey Kotchman in the second inning, Lester, who threw 54 pitches (38 strikes), retired the final 11 batters he faced.
Marlins non-roster invitee Kevin Slowey had a mixed results afternoon. He struck out five in three innings, but the right-hander gave up three runs on two hits with two walks and a hit batter.
Slowey is competing for the fifth starter or long reliever role.
Bradley jumped all over Slowey's first pitch of the game and drove an opposite-field homer to left.
Slowey regrouped and struck out four of the next six he faced.
The Marlins tied it at 1 in the first. Juan Pierre singled and scored on Chris Valaika's RBI single to right.
In the third inning, Boston regained the lead on Jarrod Saltalamacchia's two-run double. The Red Sox received a scare in the inning when Mike Napoli was plunked on the left hand by a Slowey fastball. Napoli was tended to by the trainer, but he remained in the game.
Miami turned to Tom Koehler in the fourth inning, and the right-hander was greeted much the same way as Slowey. Like Slowey, Koehler surrendered a homer to the first batter he faced.
Carp connected on a home run to left to open a two-run fourth. Bradley added an RBI double in the inning.
Up next: Opening Day starter Ricky Nolasco gets the start on Tuesday against the Astros' at Roger Dean Stadium. In the 1:05 p.m. ET contest, Houston is starting Bud Norris.