Ross (3-5) handled the Reds on four hits and four walks while striking out six en route to his third win in four starts.
Luke Gregerson twirled a scoreless eighth inning and Huston Street turned in a 1-2-3 ninth for his 22nd save as the Padres evened their three-game series.
Wil Venable later added a solo homer for the final margin.
The Reds' Tony Cingrani (5-2) was tagged with the loss, allowing just the two unearned runs on two hits over five innings.
Brandon Phillips got the only RBI for Cincinnati, which had a three-game winning streak snapped.