Belt hit his eighth spring home run, Bumgarner threw five solid innings and the reigning World Series champions, with largely the same team as a season ago, wrapped up their spring training in Arizona with an 8-6 victory over the Diamondbacks on Wednesday.
Hunter Pence also homered for the Giants. Nick Noonan, trying to make the team, had a triple, double and single for the World Series champions, who open a three-game exhibition series against Oakland on Thursday night in San Francisco.
Bumgarner, the No. 2 starter in the Giants' rotation, allowed two runs on six hits, striking out six and walking one.
Belt's solo shot off Heath Bell was his fourth homer in his last four games.
"I met all my goals," Belt joked about his big spring.
"I hope he hits another one before the All-Star break," Bumgarner deadpanned.
That's the kind of loose, confident attitude the Giants take into their season opening series next week against the Dodgers in Los Angeles.
"It was a different spring with the WBC (World Baseball Classic)," Giants manager Bruce Bochy said, "but the boys are ready to get back home and get the season started. ... You get to the last 10 days guys are getting a little eager to get going. That's where they've been lately."
Alfredo Marte, also in a competition to make the opening day squad, and Nick Ahmed homered for Arizona, playing its final spring training home game at Salt River Fields.
Arizona reliever Heath Bell gave up a two-run homer to Francisco Peguero and Belt's solo shot in the fifth. Ahmed hit a solo homer off Bumgarner in the second.
Bumgarner makes his first start of the regular season Tuesday against the Dodgers in Los Angeles. Matt Cain is San Francisco's opening day starter at Dodger Stadium on Monday.
Bumgarner, who finished the spring 2-0 with a 2.29 ERA, seemed less than thrilled with his outing, saying it was all right "except for leaving some balls over the middle."
"I just kind got lazy and lost a little bit of focus and they did what they're supposed to do with it," he said.
Bochy said his left-hander was too harsh in his self-assessment.
"He's demanding of himself but that was a pretty good game," Bochy said. "Here in the Cactus League in this park, the ball was flying, that was a pretty good game."
Arizona's Nelson Figueroa, the winning pitcher when Puerto Rico eliminated the United States in the World Baseball Classic, allowed four runs on six hits in four innings. Probably headed for a minor league assignment at Triple-A Reno, Figueroa struck out four without a walk but had a wild pitch.
Pence hit his third home run of the spring with a two-out solo shot to left in the third.
Guillermo Quiroz drove in two runs with a double and sacrifice fly for the Giants.
Bochy says he's optimistic that Pablo Sandoval could be ready for the season opener after the big third baseman went through an array of batting and fielding drills and played catch from 75 feet on Friday. He could see action in the weekend series against Oakland. Sandoval has been sidelined since March 16 because of an inflamed nerve in his right elbow. ... On Thursday night, the Giants send Tim Lincecum against the A's Tommy Milone. ... The Diamondbacks play Texas in Surprise on Thursday, then play two preseason games against Cincinnati at Chase Field in downtown Phoenix.