Fielder, 25, became the first Milwaukee player win the Derby, held on the eve of Tuesday's All-Star Game. He had six homers in the final round to five for Cruz.
Fielder led the way with 17 homers going to the final round, while Cruz had 16.
Fielder totaled 23 homers for the night, while Cruz had 21.
Philadelphia first baseman Ryan Howard, the 2006 champion, had 15 total homers.
Fielder, who is an All-Star for the second time in his career, participated in the 2007 Derby and was eliminated in the first round. Fielder's father, Cecil, was in the Home Run Derby in 1990, 1991 and 1993.
St. Louis first baseman Albert Pujols, who went into the All-Star break leading the majors with 32 homers, was eliminated in the second round Monday.
Copyright 2009 by United Press International.