Rich Aurilia, the 13-year veteran who started at third against the Pirates, homered in the fourth inning to open the scoring. And, shifting the competition to another area, right fielder Nate Schierholtz, who's pushing for playing time in a crowded outfield, hit his first Major League home run in the eighth inning to fend off Pittsburgh.
The infield corner mix includes .351-hitting Pablo Sandoval, who delivered a two-run pinch-hit single in San Francisco's big seventh, and first baseman Travis Ishikawa (.271). Every day is a proving ground for numerous Giants.
But the Giants' immediate concern Saturday was ending Pittsburgh's spell of 14 victories in 16 games against them.
Trailing, 4-1, the Giants roused themselves with one out in the seventh as pinch-hitter Dave Roberts drew a walk from reliever Denny Bautista (4-2). Randy Winn doubled, setting up Sandoval's key pinch-hit.
Sandoval, who advanced to second base on the throw home following his single, moved to third on Aurilia's groundout and scored the tying run on Bautista's wild pitch.
Bengie Molina, who went 3-for-4 on his bobblehead night, singled and was replaced by pinch-runner Eugenio Velez. Up came McClain, the 36-year-old who on Wednesday became the oldest position player in 53 years to hit his first Major League home run. The veteran of 19 professional seasons collected his second round-tripper by whacking left-hander John Grabow's first pitch into the left-field seats.
"I think that one felt a lot better than the first one, to be honest, especially to do it here in San Francisco and put us ahead," McClain said.
McClain didn't dwell on big-picture issues such as his future with the Giants ("Being 36, who knows how far my future goes in this game?") or the impact of Gillaspie's sudden arrival ("I know what they're trying to do here. It didn't surprise me in a way.").
Pittsburgh narrowed its deficit on pinch-hitter Doug Mientkiewicz's eighth-inning RBI single off Brian Wilson. But Wilson hung on for his 37th save, with help from Schierholtz's leadoff homer in the Giants' half of the eighth off Jesse Chavez.
"In most parks I think it would have been a no-doubter. Here, you never really know," said a grinning Schierholtz, acknowledging AT&T Park's tendency to discourage left-handed-batting sluggers.
In contrast to McClain, who fielded questions about his future, Schierholtz addressed his past -- specifically, his inability to hit a homer in 112 at-bats with the Giants last year. Schierholtz's dormant power concerned some talent evaluators, but the Olympian, who was recalled Tuesday, never lost faith in himself.
Schierholtz attributed his improvement to a revised plate approach. "I'm a little more relaxed and comfortable," he said. "It makes a big difference."
The Giants were fortunate that an umpiring glitch didn't make a difference. With Molina on second base and McClain on first and nobody out in the fourth inning, Aaron Rowand hit a line drive to Pittsburgh shortstop Luis Cruz, who jumped for the ball and apparently misjudged it. It went off his glove, but he quickly recovered the ball and flipped it to second baseman Freddy Sanchez. By then, Molina had returned to second and McClain was running toward the base. Both runners were ruled out.
But crew chief Tom Hallion admitted to a pool reporter later, "What the correct call should have been is, Bengie should have been allowed to stay on second, because when the second baseman received the throw, Bengie was standing on second base, which removes the force play."
None of this mattered, due to the combination of the Giants' late offense and Wilson, who weathered another Pirates run in the ninth to record his seventh save of more than one inning this year and his second career five-out save. The other came on Aug. 25, 2007, against Milwaukee.
"I've been whining about not pitching all week, and what do I get? A five-out situation," said Wilson, who hadn't pitched since Tuesday. "Be careful of what you wish for. But if my job is to get five or six outs, I'll do it."