SCOTTSDALE, Ariz. — Travis Ishikawa moved a little closer Saturday to becoming San Francisco's starting first baseman.

Ishikawa hit his third home run of the spring and went 2-for-3 in the Giants' 8-4 loss to the San Diego Padres.

"He's done all he can do," Giants manager Bruce Bochy said. "I can't predict the future. It's fair to say the way things are shaping up, he's going to be out there playing first base" when the regular season begins April 7.

Ishikawa, who raised his spring batting average to .324, connected in the fourth inning against Jae Kuk Ryu. He came to camp as the favorite for the first base job after he hit .274 with three homers in 95 at-bats with the Giants last year.

"I still feel like it's my job to lose," Ishikawa said. "I do have to show them that I look like I'm ready for the job."

Chase Headley and Nick Hundley had two-run doubles for the Padres, and non-roster invitee Kyle Blanks added a two-run homer.

Headley went 2-for-3 and Kevin Kouzmanoff had two hits to raise his spring average to .450.

Matt Cain allowed five runs and seven hits in 4 1-3 innings for San Francisco. He struck out seven and walked two.

Two of the runs charged to Cain came after he left the game, when Headley doubled in a pair. Headley leads the Padres with eight RBIs.

"You hear guys talking about getting their work in, you have to get used to going four, five, six innings. You have to get your mind and body ready for it," Cain said.

San Francisco closer Brian Wilson retired all three batters he faced in the ninth for his fifth consecutive scoreless inning of the spring.

Giants catching prospect Buster Posey hit a two-run drive in the ninth for his first homer this spring.

Posey, who got a $6.2 million signing bonus after he was selected with the fifth pick of the 2008 draft, is hitting .385 with five RBIs in 13 at-bats.

Notes: San Francisco OF Nate Schierholtz singled in two at-bats while playing in his first game since Feb. 28. Schierholtz suffered a hamstring injury a few days before spring training began, then was found to have a disk issue in his lower back. Schierholtz will not play today, Bochy said, but likely will return Monday.