HOUSTON -- Facing a left-handed starter typically means changes in the Giants' lineup. Wednesday's game against Randy Wolf and the Houston Astros likely will be no exception.

Jose Castillo, who's hitting .105 (4-for-38) in his last 10 games, is expected to start at third base for the first time since Sunday.

"Jose is trying to get his swing back," manager Bruce Bochy said. "It's fair to say that he's struggling."

To maximize the Giants' right-handed presence against Wolf, Rich Aurilia will move to first base. In contrast to Castillo, Aurilia's batting .311 (14-for-45) in his last 18 games.

Starting Aurilia will provide a break for rookie John Bowker, who's mired in a .120 skid (9-for-75).

"Johnny's having a tough time right now," Bochy said. "He has to adjust a little bit and discipline himself a little better."

Bochy pointed out that the plethora of foul balls Bowker yanked into the stands behind first base in Monday's series opener reflected that he's "pulling off" pitches.

Meanwhile, Triple-A Fresno first baseman Travis Ishikawa (.312 entering Tuesday) and Double-A catcher-first baseman Pablo Sandoval (.339) are thriving. Asked if he and general manager Brian Sabean have considered alternatives to the slumping Bowker, Bochy said, "It's something Sabes and I have talked about. We'll leave it at that."

Whatever the Giants do, they already know that lack of production at the infield corners has hampered their offense. San Francisco's first basemen began Tuesday ranked last in the National League with 10 home runs and a .364 slugging percentage. They also were next-to-last in RBIs (51), batting average (.243) and on-base percentage (.304). Giants third basemen were last in the NL in homers (eight), RBIs (37) and on-base percentage (.295).

"We definitely need more production than what we're getting," Bochy said.

Pitching matchup
SF: LHP Barry Zito (6-14, 5.55 ERA)
Zito was marred by a five-run third inning that cost him the game against the Dodgers on Friday at AT&T Park. The lefty allowed a solo homer to Danny Ardoin and a three-run double to Jeff Kent and exited after five innings. Zito said his velocity was down, but it was his changeup that did him in. He gave up two doubles on hanging changeups and only struck out one batter in the outing. Zito is 1-0 with a 2.77 ERA in two career starts against the Astros.

HOU: LHP Randy Wolf (7-10, 4.67 ERA)
Wolf took a no-decision in his most recent outing versus Cincinnati, allowing four runs over six innings in a game the Astros won in extras. Wolf faced the Giants twice this year as a member of the Padres' pitching staff. He did not earn a decision in either outing but compiled a 2.25 ERA, allowing three earned runs over 12 innings. Lifetime versus the Giants, Wolf is 5-4 with a 3.80 ERA over 12 starts.

Tidbits
Three left-handers in the Giants organization took no-hitters into the sixth inning Monday night. Jonathan Sanchez's effort at Houston was the most conspicuous, but he was joined by San Jose's Clayton Tanner and Augusta's Scott Barnes on the Class A level. ... Elsewhere in the Minors on Monday, freshly signed third baseman Conor Gillaspie drove in five runs for the Giants' club in the Arizona Rookie League. ... Sanchez, who didn't speak to reporters after Monday's game, explained that he charged Brandon Backe's sixth-inning bunt too enthusiastically. The play went for a single, helping Houston score twice. "I should have waited for the ball," Sanchez said. "That was the game right there."

Tickets
 Buy tickets now to catch the game in person.

On the Internet
 MLB.TV
 Gameday Audio
•  Gameday
•  Official game notes

On television
• CSN-BA

On radio
• KNBR 680

Up next
• Thursday: Giants (Kevin Correia, 2-6, 5.21) at Astros (Brian Moehler, 8-4, 3.83), 11:05 a.m. PT
• Friday: Giants (Matt Cain, 7-9, 3.67) at Braves (Jair Jurrjens, 11-7, 3.18), 4:30 p.m. PT
• Saturday: Giants (Jonathan Sanchez, 8-9, 4.53) at Braves (Mike Hampton, 1-1, 8.10), 4:00 p.m. PT