Lester allowed two hits while walking none and striking out four. In Grapefruit League action, Lester went 4-0 with a 0.75 ERA.
"Just really tuning up," Lester said. "That was really the main thing today. There's still first-pitch strikes and getting ahead of guys. I wanted to flip some curveballs and some changeups early in the count. We didn't get to the changeup as much as the curveball. But the main thing is get a good warmup, get stretched out -- and to get through it. It sounds bad, but that's really what you want to do, especially with these last couple -- get through them healthy and be ready for the next one."
Jonny Gomes belted a solo home run for the Red Sox in the bottom of the second.
Marlins right-hander Kevin Slowey went five innings and allowed five hits and a run, walking three and striking out four.
Daniel Bard, who is in a battle to win the final spot on Boston's pitching staff, had a rough inning of work, giving up three hits and three runs while walking a batter.
Marlins shortstop Adeiny Hechavarria went 2-for-4.
Up next: Right-hander Clay Buchholz, who will break camp as Boston's No. 2 starter, makes his last Grapefruit League outing in Thursday night's 7:05 ET game on MLB.TV against the Twins at JetBlue Park. Alfredo Aceves, Joel Hanrahan and Koji Uehara will work out of the bullpen. Outfielders Jacoby Ellsbury (jammed right heel) and Shane Victorino (right wrist) are expected to return to the lineup.