OAKLAND -- Brett Anderson boasts an unassuming presence.

His stuff, not so much.

The A's lefty, who turned the tender age of 22 less than three months ago, has quietly turned into the club's most steady rotation presence after just one full season in the big leagues.

Ever since he made his Major League debut against Seattle on April 10 last year, Anderson has left many around the baseball community wondering if he owns the staff's best stuff.

On Thursday, a day that fell just two days short of his one-year big league anniversary, Anderson yet again sent many to the water cooler after tossing six shutout innings in a 6-2 win over the Mariners.

"He was probably our most consistent guy all spring, and he took that into this afternoon's game," manager Bob Geren said. "I thought the game a year ago from today, you can see the improvement he's made. He was young and talented and good, but now he's really adding more weapons to his game.

"He's controlling his fastball, his breaking ball and his changeup on both sides of the plate, which he didn't do early last year. That part of his game came in the second half, and he showed it in his first start today."

Anderson mowed down the Mariners' lineup with the same ease he carried through his final 17 starts last year -- during which he compiled an 8-4 mark and a 2.96 ERA after going 3-7 with a 5.74 ERA in his first 13 starts.

Just don't count on the pitcher to tell you how good he's gotten. The scary part about Anderson's talent, Geren said, is that he doesn't realize that it's there most of the time. Cue in Thursday's less than mild reaction.

"The results were good," Anderson said, "but my stuff was just OK. I didn't panic and when I did fall behind, I was able to make my pitches and get some ground balls."

The left-hander's modest ways couldn't take away from the numbers that earned him a standing ovation upon his exit in the seventh inning, when right-handed reliever Chad Gaudin made his 2010 debut and erased what Anderson deemed "that big mess I made out there" -- otherwise known as runners on first and second with no out.

Gaudin retired the next three batters in order to preserve Anderson's first win of the season and reward a productive A's offense for their own efforts in the series finale.

Daric Barton led the way with three hits and a career-high four RBIs while Ryan Sweeney and Cliff Pennington also drove in runs courtesy of doubles. The latter, along with Rajai Davis and Mark Ellis, collected two hits in the game as the A's tallied 11 total -- six of which came off Seattle starter Doug Fister in the first four frames.

Barton's .337 mark when facing Seattle is his best against any team, and he proved not only to the A's community, but to himself on Thursday that he can hit just as well as he can walk.

"He had great at-bats all spring," Geren said of Barton, who broke camp batting .265 in 21 games while leading the Majors with 22 walks. "He had a very good strike zone, and the key to hitting -- no matter if you have a good swing or a mediocre swing -- is pitch selection. Daric's always been real good at that.

"Controlling the strike zone and having an idea of what pitches to swing at is something that really never slumps. You may not always get hits, but you always get in good counts and can draw some walks. He came into the game with a high on-base percentage but not many hits. You knew the hits would come, and they were all big ones today."

Meanwhile, Oakland's defense proved to be just as impressive. Davis robbed Milton Bradley of a possible home run at the center-field wall in the second frame before Kurt Suzuki added another A's gem in the fifth by chasing down a foul ball off the bat of Jose Lopez in Seattle's dugout.

"I've seen Eric Chavez make that play from third base," Geren said, "but then to take a guy and do it with catcher's gear on at the catcher's position puts it right up there with some of Chavez's Gold Glove plays. It would be really hard for anybody to try to pick a catcher in baseball that can make that play."

Said Anderson: "I think only he and Paul Lo Duca can make plays like that."

Both proved to be icing on the team's 3-1 series victory over Seattle -- a mark that represents the A's best start since 2004 and one that Geren only hopes will continue.

"I think we had a real nice run in the second half last year for awhile, and that was one of the first things I tried to talk to the team about -- trying to build on how we finished," the A's skipper said. "That stretch was a really good feeling, and it came with an aggressive style of play, and it looks like that's where we're at right now.

"Now, we have to go out on the road and do it, which is always more difficult, but we're looking forward to it."

The A's head to Anaheim for a three-game set against the Angels beginning Friday before flying to Seattle for another three against the Mariners as part of a six-game road trip.