"They certainly outplayed us," Giants manager Bruce Bochy said.
Japan established itself with a three-run third inning against Giants starter Yusmeiro Petit. The Classic's two-time defending champions amassed 10 hits by the sixth inning at Scottsdale Stadium.
"They're not known for their power, but they drove some balls well today," Bochy said.
Japan complemented its lively offense with resolute pitching. No. 1 starter Masahiro Tanaka struck out three in two innings. Seven relievers worked an inning apiece and combined to allow one run and two hits. The Giants struck out 10 times while collecting five hits.
Bochy observed that his hitters looked passive.
"Sure, we hadn't faced those guys, but you still have to get aggressive and for some reason we weren't today," Bochy said. Referring to Japan, he added, "Give them credit, though. They pitched well. They played well."
Infielder Kensuke Tanaka, the former Nippon Ham Fighters star who's trying to make the Giants' Opening Day squad as a non-roster invitee to camp, appreciated what he saw from his countrymen.
"They've been playing a lot of dedicated baseball," Tanaka said. "If they continue playing that dedicated baseball, they can be successful."
Trailing, 1-0, Japan received back-to-back singles from Sho Nakata and Hisayoshi Chono to begin its third-inning uprising. Takashi Toritani drove them both home with a double to right-center field. Toritani scored on Seiichi Uchikawa's two-out infield hit.
Nakata's triple, Shinnosuke Abe's single and ex-Major Leaguer Kazuo Matsui's sacrifice fly drove in Japan's runs in the fourth through sixth innings, respectively.
Francisco Peguero, bidding for a reserve outfield spot, accounted for most of San Francisco's offense. His single to center field, which grazed Masahiro Tanaka's glove, gave the Giants their temporary lead in the second inning. It followed Hunter Pence's leadoff infield single, Johnny Monell's walk and Kensuke Tanaka's fielder's-choice grounder.
Peguero added a sixth-inning sacrifice fly to generate another Giants run, which was unearned due to right fielder Yoshio Itoi's two-base error on Roger Kieschnick's fly ball that opened the inning. Gary Brown belted a solo homer in the ninth.
Up next: The two-time World Baseball Classic title-winning squad will continue preparing for the Classic semifinals in San Francisco by facing a split squad of Chicago Cubs in Mesa on Friday. Left-hander Travis Wood will start against Team Japan.