Adam Conley (4-3) earned the win, allowing five hits, two walks and two runs in a season-high 7 2/3 innings. He is 3-0 in three career starts against Cincinnati.
The Marlins (49-53) have won four straight games and seven of their past nine. They will go for a four-game sweep of the Reds on Sunday.
Meanwhile, Cincinnati (41-63) has lost six games in a row and is 14-16 since the All-Star break. The Reds have dropped eight straight games at Marlins Park.
Tim Adleman (5-9) gave up six runs, six hits and four walks in 4 1/3 innings. He has allowed at least one homer in 12 straight games.
The Reds opened the scoring with two outs in the first. Joey Votto hit his 27th homer of the season, a solo blast to center.
That lead was quickly erased. With two outs in the third, Yelich hit an 0-2 pitch for his opposite-field homer, sending the ball to left-center field for his 12th home run of the season.
Cincinnati cut its deficit to 3-2 in the fourth inning when Adam Duvall hit his 23rd homer of the season, a drive to left.
Conley’s leadoff walk started what became a three-run rally in the fifth. Dee Gordon singled, and Giancarlo Stanton hit a two-run double to right-center.
Marcell Ozuna capped the inning with an RBI double that sailed over the head of center fielder Billy Hamilton, giving Miami a 6-2 lead.
NOTES: Cincinnati placed All-Star SS Zack Cozart (quad) on the disabled list. The Reds recalled RHP Kevin Shackelford, a reliever, from Triple-A Louisville. He pitched two innings Saturday and allowed one run, striking out three. … RHP Brad Ziegler (back injury) came off the disabled and was made the Marlins closer, replacing A.J. Ramos, who was traded late Friday night. Ziegler, 37, has 85 career saves but has struggled this year with a 6.52 ERA. Ramos, 30, has 92 saves since the start of the 2015 season. He was an All-Star last season when he saved 40 games and posted his third straight season with an ERA under 3.00. His 90.9 save percentage this season is ranked fifth in the majors among relievers with at least 20 saves. … Sunday’s series finale features Marlins RHP Dan Straily against Reds RHP Luis Castillo. This will be the first time they have faced their former teams since they were traded for each other in January.