Harrison Bader scored two runs for the Reds, who have won the first two games of the three-game series. Daniel Duarte (2-0) picked up the win with a scoreless inning of relief. Alexis Diaz pitched a hitless ninth for his 36th save.
Cincinnati starter Connor Phillips gave up three hits, four hits and four walks in four-plus innings. He struck out three. The Reds (76-71) climbed into a tie with the Arizona Diamondbacks (76-71) for the third and final National League wild-card spot.
Spencer Torkelson hit a two-run homer for the Tigers (66-79).
Detroit starter Eduardo Rodriguez (11-8) allowed four runs, four hits and a season-high five walks in 5 1/3 innings. He fanned five. Alex Faedo gave up just one hit in three scoreless innings for the Tigers, who left 13 on base and went 1-for-13 with runners in scoring position.
The Reds jumped on top in the second inning. With one out, Christian Encarnacion-Strand singled and Bader walked. Friedl ripped a two-out, two-run triple down the right field line to bring home both runners.
Detroit evened the score in the third. Zach McKinstry drew a leadoff walk and scored on Torkelson's 28th homer, a one-out shot that barely cleared the right field wall.
Cincinnati regained the lead at 4-2 the next inning. Bader walked, Noelvi Marte singled and Friedl reached on a bunt hit to load the bases with no outs.
A fielder's-choice grounder from Luke Maile scored Bader. Jonathan India then struck out, and when Maile took off running, catcher Carson Kelly tried to throw him out. Maile retreated long enough to allow Marte to score before he was tagged out.
Detroit got one of those runs back in the bottom of the inning. Parker Meadows walked, stole second and scored on Akil Baddoo's opposite-field double.
The Tigers had the bases loaded with two outs in the fifth before Meadows was retired on a comebacker to reliever Sam Moll.
Detroit stranded two runners in both of the sixth and seventh innings.
With a runner on second and two outs in the ninth, Meadows lined out to first base to end the game.
—Field Level Media