OAKLAND -- As part of their celebration of the 1989 World Series champions, the A's on Monday gave 10,000 fans a Mark McGwire replica jersey.

Star-crossed infielder Bobby Crosby, who spent the first six weeks of 2009 working on his swing with McGwire in Southern California, helped give the A's a feel-good victory.

Crosby, who lugged a .194 batting average into the game, broke open a tight game by driving in the final three runs of Oakland's 5-1 win over the visiting Giants in the opener of a three-game Interleague series.

San Francisco swept the A's at AT&T Park last weekend, holding them to three runs in three games.

"They're a good team, and they stuck it to us at their place," Crosby said. "Hopefully we can get a couple more wins here the next couple nights and give it back to 'em."

In matching his season high in RBIs, twice driving home former Giants outfielder Rajai Davis, who had a big game of his own, Crosby made sure that one of rookie right-hander Trevor Cahill's best outings of the year did not go wasted.

Cahill, whose first six weeks as a big leaguer were marked by wild inconsistency, has been anything but inconsistent since taking a pounding in Detroit on May 17.

In his past seven starts, he's posted a 2.44 ERA, allowing more than two earned runs just once, and with seven innings of four-hit work against the Giants, he evened his record at 5-5.

He walked one, struck out four and saw his line sullied only by the Travis Ishikawa home run that opened the scoring with two out in the second inning.

"Pitching is repeating your delivery," Cahill said. "I'm doing a lot better at that now."

According to A's manager Bob Geren, Cahill is doing a lot better at just about everything these days.

"Early in the year, he was kind of all over the place," Geren said. "His arm angle was different on different pitches, his arm slot, his times [to the plate]. ... Now, he's under control with everything."

To emphasize his point, Geren noted that Cahill did a fine job Monday of controlling the Giants who managed to reach base against him. Cahill confirmed that he's been working on that part of his game and suggested that it's a difficult balance.

"You don't want guys to steal bases," Cahill said. "But you don't want to make terrible pitches, either."

Stealing bases is a specialty of Davis, who was waived by the Giants early last season. The A's picked him up and fell in love with his speed, which was on display in various forms Monday.

Davis bunted for a single and stole second before scoring on Crosby's game-breaking, two-run double in the sixth, and he tripled before scoring on a Crosby groundout for a big insurance run in the eighth.

He insists that playing well against the Giants doesn't give him any more satisfaction than playing well against, say, the Royals. Or the Rangers. But Davis did allow himself a little dig-me moment when asked if it was sweet to fly around the bases while his former teammates chased his three-bagger into the right-center gap.

"Oh, absolutely," he said with a smile.

Oakland countered Ishikawa's homer off the top of the out-of-town scoreboard in right field with two runs in the fourth. Jack Cust and Matt Holliday singled and walked, respectively, to open the inning, Orlando Cabrera hit the first of his two doubles on the night to score Cust, and Ryan Sweeney grounded out to score Holliday.

Crosby's big double, which he poked down the right-field line off Giants lefty Jonathan Sanchez, helped the A's get their 10th win in 26 games this year against a southpaw starter.

"We didn't really do a lot of damage, but we put the ball in play when we needed to," Geren said. "Lefties have been tough on us, but we got to one a little tonight."

The Giants did no such thing against Cahill, whose heavy sinker and ability to command the ball on both sides of the plate belie his age -- 21 -- and appearance. While doing a postgame interview, he looked like a high school junior on the nervous night before prom.

"He had a good sinker. ... That's what he's known for," said Giants rookie second baseman Matt Downs. "He had it working. He mixed it in well and got a lot of groundouts."

Added San Francisco outfielder Nate Schierholtz: "He pitched us well. He kept his sinker down all night, and we chased it."

The final word, though, goes to Crosby, whose new-for-2009 role of utility infielder has allowed him to see Cahill work from all over the diamond.

"If he keeps the ball down, he has some of the best stuff in the big leagues," Crosby said. "He really does."