Scherzer (8-5) controlled the Royals on one run, yielding five hits and a single walk while striking out seven.
The right-hander won for the third time in four starts as the Tigers completed a three-game series sweep at Comerica Park.
With Detroit leading 3-1 in the fifth, Fielder crushed the first pitch he saw from Tim Collins deep into the right-field bleachers, breaking the game open.
Jhonny Peralta went 3-for-4 with a two-run homer and three RBI in the victory.
Royals starter Everett Teaford (1-2) was roughed up for five runs on seven hits in a 4 1/3-inning effort.
Salvador Perez socked a solo homer for Kansas City's only run.