A brisk win helped Belt's homer clear the left-field fence.
"I hit it pretty good, but I popped it up a little more than I thought," Belt said. "I'd rather get lucky and be 1 for 3 rather than be unlucky and be 0 for 3."
Belt drove in all three Giants' runs. He hit a sacrifice fly to tie the game 3-3 in the eighth inning. He drove in Gregor Blanco, who had doubled.
Blanco went 2 for 4 to raise his average to .444 and scored two runs.
Luis Cruz belted a homer to left field that broke a 2-2 tie in the sixth for the Dodgers.
Los Angeles starter Aaron Harang gave up seven hits and two runs, including Belt's homer, in four innings.
"It's hard to judge because of the way the wind is blowing," Harang said. "You come out of a 2-1 game in those conditions. ... I felt good.
"There are a few ballparks in the league where you'll get these kind of conditions. ... Fly balls are carrying or the wind is knocking them down. You get your pitches out of it, try to work on throwing strikes."
Fielders such as Belt, a first baseman in the past who is learning left field, had the same sort of intrigue.
"I'm just learning how to get my routes down and take good angles. You add the wind factor, and it makes it a lot tougher."
Starter Brian Burres limited the Dodgers to one run and three hits in three innings.
A sellout crowd of 13,655, a Cactus League record, attended in the breezy conditions. A storm approaching from the west threatens Cactus League games on Sunday, including a sellout at Camelback Ranch in which the Dodgers host the Los Angeles Angels of Anaheim.
"From what we've heard we'll be able to play," manager Don Mattingly said. "If we don't play, we'll hit in the cages and work out."
The Dodgers had a chance to win the game in the bottom of the ninth.
Then Matt Yourkin, who pitched three scoreless innings to lower his ERA to 2.25, struck out Justin Sellers to end the game.
Dodgers infielder Ivan DeJesus Jr. injured his side while swinging. He will undergo tests, Mattingly said.
"He's been looking great," Mattingly said of DeJesus, who has been stellar in the infield.
Don Newcombe, the Dodgers' special adviser to the chairman, threw out the ceremonial first pitch. Newcombe threw a strike. ... Vin Scully, who hadn't broadcast a game since Sept. 28, worked Saturday night's game for Dodgers' TV. Scully, who is entering his 63rd season as a Dodger broadcaster, said he needed some "batting practice." Scully, 84, is eliminating games in Colorado from his schedule this season "just to cut back a little bit more on the traveling." He will broadcast games in California and Arizona, more than 100 games in all. The first three innings will be simulcast on radio.