Fielder's big blow came in the second inning and gave Detroit a 4-1 lead. With the three RBI, the Detroit first baseman increased his total to 51, third-best in the American League behind teammate Miguel Cabrera (67) and Baltimore's Chris Davis (52).
Andy Dirks added a pair of run-scoring singles for the American League Central-leading Tigers, who took a second straight from second-place Cleveland and extended their lead over the Indians to 4 1/2 games.
Porcello (3-3) handled the Tribe on three hits and two walks, allowing two runs (one earned). The right-hander struck out seven.
Jose Valverde pitched a scoreless ninth for his eighth save.
Cleveland starter Carlos Carrasco (0-2) was roughed up for six runs on 10 hits in a four-inning effort.
Ryan Raburn knocked a two-run homer en route to three RBI for the Tribe, who fell below .500 (30-31).