Belt was 3-for-5 and and keyed the defending World Series champions' six-run seventh inning with a bases-clearing double in San Francisco's 10-9 win over Milwaukee's split squad.
Making his first start in the Cactus League, Belt scored twice and got the Giants on the board with a second-inning RBI single. The 22-year-old entered the day 0-for-2 after pinch hitting in two previous spring games.
"Obviously I have a little bit more confidence now," Belt told MLB.com. "The past few games I was coming in late, getting an at-bat a game. I was probably pressing a little bit because I wanted to get that first hit. But today I could kind of relax a little bit more and just do my thing, since I knew I was going to have a couple of at-bats. Now I just have to be consistent with that."
Drafted in the fifth round by the Giants in 2009, Belt made a splash in his debut, batting .352 in 136 games between Class A Advanced San Jose, Double-A Richmond and Triple-A Fresno. He was the second Minor Leaguer in 2010 to hit 20 doubles, 20 homers and steal 20 bases on Aug. 25, and he was named MLB.com's No. 26 prospect in late January.
Catcher Thomas Joseph, a second-rounder in 2009, was 1-for-2 with a run scored as a pinch-hitter and Thomas Neal scored a run.
Giants non-roster invitee Marc Kroon, who was originally drafted by the Mets in 1991, allowed two runs in an inning of relief as he tries to get back to the Majors for the first time since 2004.