The Giants' No. 5 prospect homered twice and plated three runs as Double-A Richmond beat Bowie, 4-2.
Joseph, who also doubled, got the Flying Squirrels on the board early, slugging a two-run homer in the first inning. With Richmond holding on to a 3-1 lead, the 20-year-old catcher launched a solo blast in the fifth.
"I just kind of went up there and looked for something up in the zone that I could drive and get an early lead for the team," Joseph said of his first homer. "Fastball in the middle of the plate and I put a good swing on it and it just happened to go over the fence."
A second-round pick in the 2009 Draft, Joseph entered Monday's contest batting .229 with a homer and four RBIs in 17 Eastern League contests. This was the fifth two-homer game of the Arizona native's career, with the most recent coming on Sept. 3, 2011 for Class A Advanced San Jose.
"Our hitting coordinator Steve Decker is in town. I was working with him and our hitting coach Ken Joyce and Minor League coordinator Shane Turner on staying short and quick to the ball. I think it paid off in the game," Joseph said. "It was definitely one of the better games I've had. Obviously as a hitter, you enjoy hitting homers and having success tonight was definitely fun."
Joseph, who batted .270 with 22 homers and 95 RBIs in 2011, hasn't set personal goals for himself, preferring to focus instead on the success of the Flying Squirrels, who are 12-12 and in third place in the Western Division.
"I'd much rather win a championship in the Eastern League than be the MVP, so [I will do] everything I can do to help my team do that."
Gary Brown, the club's top prospect, reached base twice and drove in a run.
Chris Heston, a California League All-Star in 2011, improved to 2-2 after allowing a run on three hits while fanning eight over 5 1/3 innings for Richmond.
Manny Machado, MLB.com's No. 6 prospect singled home a run for the Baysox.