Todd Frazier had a season-high four hits and Devin Mesoraco hit a two-run single for the Reds, who had 15 hits and took three of four games in Miami. They improved to 5-11 since the All-Star break and scored more than five runs for the first time during that stretch.
The Marlins managed only eight runs and 24 hits in the series, and have lost to Cincinnati in eight of their past nine games.
Mike Leake (9-9) allowed one run in six innings. He has won all three of his career starts against the Marlins.
Zack Cozart's two-out RBI single in the second put Cincinnati ahead. In the third inning, Hamilton and Jay Bruce each singled, stole second and scored. Bruce singled home Hamilton and scored on a double by Ryan Ludwick.
Two-out, run-scoring singles by Hamilton and Frazier in the fourth made it 5-0. The Reds went 7 for 18 with runners in scoring position.
Garrett Jones hit his 12th homer for the Marlins, who totaled five hits. They went 1 for 9 with runners in scoring position.
Stanton, the NL leader in home runs and RBIs, struck out four times for the second Sunday in a row. Stanton also robbed Kristopher Negron of an RBI extra-base hit when he made a long run for an over-the-shoulder catch near the right-field foul pole in the second inning.