After heading into the ninth inning up 1-0, the Reds gave up a two-run home run to William Contreras in what was looking like another late-inning Brewers comeback.
But the Reds put a stop to the league's best team.
After Will Benson reached third thanks to a Noelvi Marte single, Jose Trevino knocked in his second RBI of the game to tie it all up 2-2 in the bottom of the ninth, sending it to extra innings.
Reliever Graham Aschraft came in for the Reds in the top of the 10th to throw a hitless inning on 10 pitches.
Then, after the Reds loaded the bases, outfielder Austin Hays brought in the winning run to the plate.
Reds starting pitcher Andrew Abbott tossed seven shutout innings (92 pitches) against the hottest-hitting team in baseball, giving up just four hits while striking out seven and walking none.
It's Abbott's fifth shutout of the year and his first since June 10th, bringing his earned run average down to 2.28 - the second-best in all of baseball.
Cinci improves to 65-60 on the season while the Brewers earned their first loss in August, bringing their record to 78-45.
Milwaukee set a franchise record on Saturday with their 14th straight win after defeating the Reds in extra innings. Heading into Sunday's matchup, the Brewers had outscored their opponents 119-52 during the win streak.
They are now 39-10 in their last 49 games, still possessing the top record in baseball with a +161 run differential.