SAN FRANCISCO -- After his third hit, it was finally time for Buster Posey to smile. Giants first base coach Roberto Kelly joked with the rookie that he made it look easy.
"It's not that easy," Posey said.
The Giants' top prospect had three hits and three RBIs in his first major league game of the season and Juan Uribe homered and drove in two runs as the San Francisco Giants sent the Arizona Diamondbacks to their sixth straight defeat with a 12-1 victory Saturday night.
"What a great job the kid did," Giants manager Bruce Bochy said. "I'm sure he didn't much sleep last night and then he goes out and gets big hits for us. It's something we needed."
Posey played in a minor league game in Salt Lake Friday night and flew to the Bay Area early in the morning. He started a first base -- he usually catches -- and batted sixth and he received a standing ovation when he batted for the first time.
"That was great, fun and humbling," Posey said. "That's when I need to slow myself down because that's what can get me going."
Jonathan Sanchez (3-4) ended a five-game winless streak, allowing a run on two hits over five innings. He walked four and struck out seven.
"Sanchez pitched fine," Bochy said. "He really had to work in the fifth inning and got his pitch count up and that's why he had to come out. It was nice that we got some runs for him."
Eli Whiteside also hit a home run and drove in two for the Giants. Aubrey Huff, Aaron Rowand, Pablo Sandoval, Travis Ishikawa and relief pitcher Denny Bautista each added an RBI as the Giants recorded a season high for runs scored.
Billy Buckner (0-3) gave up seven runs on nine hits over four-plus innings. He walked three and struck out five as his ERA ballooned to 11.08 following his third start for the Diamondbacks.
"I haven't seen what I wanted. I wanted a win," Arizona manager A.J. Hinch said. "For a week, we've found ourselves in a rut. We're not doing a lot of things right and there's not a lot of ways to describe it."
Conor Jackson, mired in a slump, batted seventh for the first time since April 6, 2009. He went 0 for 3 with a walk and has one hit in 17 at bats on the current road trip.
Buckner walked the first two batters he faced, and both scored to give the Giants a 2-0 lead. Huff's sacrifice fly scored one run and Posey, the Giants' first-round pick in 2008, singled for his first career RBI.
"It's nice to face a guy I've seen a few times," Posey said. "I think I faced him a couple of times this year."
Rusty Ryal's third-inning home run cut the lead in half but Uribe homered in the third and Whiteside hit his home run leading off the fourth to give the Giants a 4-1 edge. Arizona pitchers have allowed a major league high 85 homers.
Consecutive singles by Sandoval, Huff, Uribe and Posey ended Buckner's night and helped give San Francisco a 7-1 edge, the best run support of the season for Sanchez.
Buckner has yet to pitch more than five innings in any of his three starts this season.
The Giants added three runs in the seventh, including Bautista's second career hit and RBI, and his first since July 7, 2008. Sandoval, who had three hits and scored three runs, and Ishikawa each doubled home a run in the eighth.
RHP Waldis Joaquin was optioned to Fresno of the PCL to make room for Posey. ... OF Pat Burrell signed a minor-league deal with the Giants and was assigned to Fresno. ... Arizona IF Kelly Johnson has a hit in five of his last six games. ... D'Backs C Miguel Montero (right knee sprain) is scheduled to face live pitching at extended spring training beginning Monday in Tucson. ... Sanchez received more than three runs of support for just the second time. ... Uribe has seven hits in 12 at bats against Buckner. ... Arizona RHP Kris Benson allowed four runs on six hits in four innings in his second rehab start for the Reno Aces. He allowed his third home run.