That brought up Fielder, who cracked on the first pitch he saw deep over the center field fence for the decisive blow.
The blast made a winner of Max Scherzer (3-0), who struck out 10 over 7 1/3 innings. The right-hander allowed three runs on six hits and didn't issue a walk as Detroit reeled off a fourth straight victory.
Dirks also went deep and Joaquin Benoit recorded the final out for his second save.
Pelfrey (2-3) yielded four runs on seven hits over 5 1/3 frames.
Josh Willingham socked a solo homer and Oswaldo Arcia went 2-for-3 with an RBI for Minnesota, which dropped the opener of a three-game road series.