The Reds built a six-run lead in the top of the first, but Yelich and Pina hit back-to-back home runs in the bottom of the inning.
Brewers prospect Keston Hiura scored Eric Thames with a two-out double to make it 6-3 heading into the second.
Yelich made it 6-4 with an RBI double in the second, while Perez homered in the third to make it 6-5.
Cincinnati scored three runs in the fourth, and tacked on two more in the eighth.
Right-handed pitcher Josh Tomlin, who signed a minor-league deal with the Brewers earlier this month, got the start, allowing seven hits and six earned runs in three innings.