OAKLAND -- Giants left-hander Jeremy Affeldt pulled his left hamstring in the eighth inning of Sunday's 3-0 loss at Oakland and left the game two batters later.

Affeldt said he felt discomfort as he dashed from the mound to field a sacrifice bunt by Daric Barton, the first batter he faced.

"It zapped me pretty good," Affeldt said.

Affeldt then yielded an RBI single to Kurt Suzuki and another single to Kevin Kouzmanoff before Dan Runzler relieved him.

Affeldt, who likely will be examined Monday, couldn't gauge the severity of his injury.

"I've never had a hamstring issue, so I don't know what to tell you," he said.

San Francisco's top setup reliever, Affeldt is 2-3 with a 3.12 ERA this season, and has converted two saves in 17 appearances.

Giants stick with regular rotation vs. Nats

OAKLAND -- The Giants will stick with their regular pitching rotation when they resume activity against the Washington Nationals at AT&T Park after Monday's scheduled off-day.

Todd Wellemeyer (2-4) will oppose ex-Giant Livan Hernandez (4-2) in Tuesday's series opener, followed by Tim Lincecum (5-0) against Luis Atilano on Wednesday. Thursday's series finale will pit Barry Zito (6-2) against Scott Olsen (2-2).

The Giants were pondering skipping Wellemeyer, the No. 5 starter, who has a 5.71 ERA. Had they done so, the other starters would have received their usual rest due to Monday's break. But Wellemeyer is 2-1 with a 3.04 ERA at home, compared with an 0-3 mark and a 9.35 ERA on the road. That may have influenced the Giants' decision, which was announced after the team left the Oakland-Alameda County Coliseum following Sunday's 3-0 loss to the A's.

Molina doesn't start in Bay Bridge finale

OAKLAND -- Catcher Bengie Molina received a break in Sunday's 3-0 loss to the A's instead of handling designated-hitter duties, as Giants manager Bruce Bochy originally intended.

Bochy decided that Molina, who began the afternoon hitless in his previous 17 at-bats, needed a respite. Molina has gone 14 games without an RBI, though he's still batting .288 overall and owns a respectable .361 on-base percentage. Entering Sunday, Molina had appeared in 35 of San Francisco's first 42 games, starting 31 of them behind the plate.

"Mentally, he could use a day [off] here," Bochy said before the finale. "We all go through our ups and downs."

Bochy also reasoned that, combined with Monday's scheduled off-day, Molina could receive the equivalent of two days off unless the Giants suddenly needed him to play extensively.

Eli Whiteside replaced Molina behind the plate and Juan Uribe, coping with tightness in his left hamstring, served as the designated hitter. Molina pinch-hit for Whiteside in the eighth and singled, and remained in the game behind the plate in the bottom half of the frame.

Schierholtz misses third successive game

OAKLAND -- Though Giants manager Bruce Bochy said Sunday that Nate Schierholtz was "playable," the right fielder missed his third consecutive start with a bruised right shoulder.

Schierholtz entered both Saturday and Sunday's games in the eighth inning and played defense, but did not bat.

"He's not quite 100 percent," said Bochy, indicating that Schierholtz again could be used off the bench in some capacity.

For the third game in a row, the Giants responded to Schierholtz's absence by moving Andres Torres to right field and inserting John Bowker in left.