SAN FRANCISCO — When the San Francisco Giants signed first baseman Aubrey Huff, the arithmetic appeared simple: Add offense, subtract defense.

But what happens when you throw solid baserunning into the equation? And how do you correct the math when he snags a line drive or catches a windblown foul pop?

Huff did all those things, and oh yeah, he also scored three runs while reaching base in all five plate appearances from the cleanup spot. The Giants offense hummed around him to support Barry Zito in a 9-3 victory over the Pittsburgh Pirates Monday night at AT&T Park.

Bengie Molina was 4-for-4 with a two-run home run as the Giants improved to 6-1 and grabbed a two-game lead in the NL West. It's the first time since July 2004 that they've held a multiple-game edge atop the division.

And Zito is 2-0 for just the second time in his 11 seasons. He improved to 106-6 in his career when receiving at least four runs, including 21-2 in 26 starts as a Giant.

He received defensive support, too. In addition to Huff's antics, third baseman Pablo Sandoval made a play down the line and second baseman Juan Uribe ranged up the middle to take away another hit.

Giants officials didn't think their defensive concessions over the winter would make a major impact because their staff led the NL in strikeouts last season. Pitchers such as Matt Cain generate a fair number of pop-ups, too.

But Zito relies on his defense. And through two starts, the eight men around him have made nearly all the plays. Zito's BABIP, or opponent's average on balls in play, is just .211 — far below his career rate of .270.

Zito wasn't perfect. He allowed three runs and didn't retire a batter in the seventh inning; old A's teammate Bobby Crosby drew a pinch walk to end the left-hander's night.

But Zito had room to operate after the Giants battered Brian Burres, who started after Ross Ohlendorf was scratched because of a bad back. Burres, a former Giants farmhand who was lost to the Baltimore Orioles on a waiver claim in 2007, gave up six runs in four innings.

Burres played with Huff in Baltimore, and by the way their confrontations went, you might assume they weren't buddies. Burres hit Huff with pitches in the first and third, and busted him hard inside on the first pitch of his at-bat in the fourth.

More likely, Burres knew it was a bad idea to throw Huff anything over the plate. That's where Burres missed, and Huff pounded it to the deepest part of right-center field for a triple.

The Giants dugout howled with laughter as Huff wearily slid into third base. One inning earlier, he had scored from first base on Bengie Molina's double. Huff ran hard in 270-foot bursts on two occasions Sunday night, too.

No wonder his teammates waved towels in front of his face.

"He was telling me this spring," Giants manager Bruce Bochy said. "He said, 'I'm not the fastest guy, but I'm a good baserunner.' Which we have to be."

Huff no doubt prefers a nice, slow trot. But he won't get the chance to do that often at AT&T Park. He posed for a moment after hitting his triple before he realized it didn't have a prayer of clearing the arcade. When the inning ended, he deadpanned and flexed a biceps as he walked to the dugout.

Huff wasn't the only free agent to make a contribution. Mark DeRosa's two-run single opened the scoring in the first inning. And Molina, the erstwhile cleanup hitter and surprise returnee, showed he's capable of knocking in runs regardless of where he bats in the order.