Trailing 2-1 entering the inning, the Tigers put Andy Dirks and Miguel Cabrera aboard with two outs against Texas starter Scott Feldman (6-7) and Fielder followed by blasting a 2-1 pitch deep into the right field seats.
Max Scherzer (11-6) collected the victory, allowing a pair of runs on eight hits over six innings. He walked two and struck out eight.
Feldman (6-7) was tagged for four runs on six hits in a 5 2/3-inning effort.
Josh Hamilton smacked his 31st homer of the year for the American League West-leading Rangers.