Bumgarner (1-1) allowed one earned run on four hits and three walks while striking out three over five innings and smacked a solo home run as Triple-A Fresno doubled up Portland, 4-2, on Sunday.
The left-hander, the top pitching prospect in the Giants system and No. 10 on MLB.com's Top 50 Prospects list, threw 99 pitches -- 58 for strikes -- in the outing.
The Beavers' Luis Durango singled to center field off Bumgarner to start his day, but Bumgarner helped pick him off. He threw to first baseman Brett Pill, who relayed to shortstop Ryan Rohlinger for the tag.
A similar scenario occurred in the second inning, as Craig Stansberry singled to center. This time, Bumgarner directly picked him off first base.
Bumgarner helped his own cause by leading off the third inning with a homer to right field. He cranked a grand slam last July 22 for the Double-A Connecticut Defenders. It was the first longball hit by a Grizzlies pitcher since Kevin Pickford hit three during the 2003 season.
He also did some fielding work. Sean Kazmar singled later in the inning and Josh Geer bunted, but Bumgarner threw to Rohlinger for the forceout at second.
Durango singled in a run in the fifth before Lance Zawadzki lined to Pill to end Bumgarner's outing.
Bumgarner gave up two runs -- one earned -- on three hits and a walk while fanning three over six innings in his last start against Portland on April 19.
That followed a couple of substandard outings that opened the season: A no-decision at Reno on April 9 (four runs on 11 hits and two walks over three innings) and a loss at Las Vegas on April 14 (seven runs on 10 hits in four frames).