The Orioles took a 3-1 lead in the fifth on a two-run shot by Matt Wieters, but Fielder came through twice in the late innings to bring the Tigers their third straight victory.
Fielder's sixth-inning homer came with one out after Miguel Cabrera had singled, and his eighth-inning shot followed a two-out walk to Cabrera. The Detroit slugger has 22 homers for the season.
Darren O'Day entered the game in the seventh for the Orioles and wound up taking the loss when he gave up Fielder's second homer. O'Day suffered his first setback of the season after winning his first six decisions.