Medlen (1-1) rebounded after a Thursday loss to Philadelphia, which snapped his string of 23 straight starts in which the Braves had won.
The right-hander yielded three hits and two walks while striking out one as the Braves (7-1) reeled off a fifth straight win and continued their best start since 2007.
Evan Gattis supplied a two-run homer and Justin Upton also drove in a run for Atlanta.
Marlins starter Wade LeBlanc (0-2) was touched for two runs on six hits and a walk over six frames.
Placido Polanco and Rob Brantly each supplied an RBI for Miami.
Swim Week Miami Beach 2014 [PHOTOS]