OAKLAND, Calif. -- The San Francisco Giants get an opportunity to ease what they hope will be a healthier Buster Posey back into the lineup as a designated hitter when they continue a six-game series against the Oakland Athletics on the American League side of the San Francisco Bay on Friday night.

Giants rookie right-hander Dereck Rodriguez (4-1, 2.89) and A's veteran righty Edwin Jackson (1-1, 2.59) are set to duel in the opener of the second half of the series, after Oakland took two of three in San Francisco leading into the All-Star break.

Posey caught all three games in San Francisco, going 4-for-12, before immediately heading to the doctor's office for a cortisone shot on his ailing right hip following Sunday's 6-2 loss.

He missed the All-Star Game in order to get four days off in preparation for a second half in which the Giants (50-48) find themselves four games behind Atlanta (52-42) in the wild-card race.

With Madison Bumgarner and Johnny Cueto fully rested and ready to go, Giants manager Bruce Bochy surprised some by announcing that Rodriguez would open the second half for his team.

"It's fair to say he's done a good job," Bochy said. "We're also breaking up our lefties and going right-left-right. All those things came to mind.

Bumgarner, a left-hander, is scheduled to go Saturday, with Cueto, a righty, slated for Sunday.

Rodriguez, an in-season call-up from the minors, hasn't allowed more than three earned runs in any of his last five starts.

The 26-year-old has never faced the A's and has never pitched in an interleague game, but certainly he's quite familiar with the latter. His dad, Ivan, was a veteran of 2,151 American League games and hit .304 as a DH in 231 plate appearances.

Posey has been even better than that in his DH opportunities, hitting .323 in 111 plate appearances.

Serving as the catcher in the National League park, Posey had a key hit in last Friday's series-opening win over the A's. His RBI single in the sixth inning off Jackson broke a 1-1 tie and sent the Giants on their way to a 7-1 win.

Jackson pitched better than the final score would indicate. He was pulled from a 2-1 game after six innings, having allowed only four hits.

The 34-year-old has allowed two or fewer earned runs in all four of his starts with the A's since being signed off the scrap heap. He's 5-5 in his career against the Giants with a 4.56 ERA in 13 meetings, including 12 starts.

The A's rebounded from last Friday's loss to win the San Francisco portion of the series with 4-3 and 6-2 victories.

Mark Canha was the key offensive weapon for Oakland in the wins, bombing a go-ahead, two-run homer in the seventh inning of Saturday's triumph, then contributing one of four consecutive A's hits to a four-run fourth inning in Sunday's win.

The A's (55-42) open the second half three games behind Seattle (58-39) in the AL wild-card race.