Belt, MLB.com's No. 26 prospect, went 3-for-4 with a homer, a double, a stolen base and two RBIs on Thursday night as Fresno edged host Salt Lake, 5-4.
After a remarkable tear through three Minor League levels last season, Belt began the 2011 campaign in the Majors, but hit just .192 in 17 games before the Giants sent him to Triple-A to work out the kinks in his swing.
It didn't take him long, as he went deep in his first game with the Grizzlies and is batting .429 with two homers and six RBIs in five games.
The 23-year-old first baseman gave Fresno an early lead with a two-run shot to center field in the first inning. After flying out in the third, he ripped a double to right in the fifth, walked in the seventh and singled in the ninth.
Second baseman Edgar Gonzalez also collected three hits and drove in two runs for the Grizzlies, who won their third straight road game.
Fresno starter Josh Banks (1-1) gave up three runs on six hits over six frames. He struck out six and walked one. Veteran closer Marc Kroon notched his fourth save by fanning two in a perfect ninth.
Jeff Baisley continued to wield a hot bat for Salt Lake, clubbing his fifth homer of the season and doubling to lift his season average to .410.
Reliever Amalio Diaz fell to 3-1 for the Bees, who have lost three in a row. He yielded three runs on one hit and one walk while striking out three in 1 2/3 innings.