Fielder has homered in 3 of his last 4 games and the Brewers have won four straight.
Jeff Suppan worked 7 innings before leaving, trailing 3-1. But the Brewers scored two unearned runs to tie it after 7, then Fielder won it in the 8th.
Saloman Torres got out of a 1-out, bases loaded jam in the 9th to save it for the Brewers.
Seth McClung pitches game two of the series tonight, against Arizona's Randy Johnson.