SEATTLE -- Trevor Cahill finished the season the way he started -- with a dominant effort.
His problem this season was a couple woeful months in between his start and finish.
"It was just an inconsistent season, I guess," said the A's right-hander. "It started off real strong and kind of went down hill from there. I've felt better the last couple starts."
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Cahill (12-14), who won 18 games last season, won six of his first eight starts with two no-decisions. But from June 30 until Aug. 30, he went 1-8 with a 6.07 earned run average.
He is 3-1 in September with a 3.56 ERA.
"After the first inning, he was dominant," A's manager Bob Melvin said. "I think that's the guy we're used to seeing."
Craig Breslow and Jerry Blevins each pitched a perfect inning to maintain the four-hitter. Josh Willingham and Scott Sizemore supplied most of the offense with home runs.
After allowing a pair of singles in the first inning, Cahill struck out Dustin Ackley and induced Mike Carp to hit into a double play. He retired 13 batters in a row and no base-runner advanced past second base. He struck out seven and walked one.
"The first two guys got on base and I was able to get out of it," Cahill said. "So that was kind of a momentum swing since we scored three in the first."
The A's got to Mariners starter Blake Beavan (5-6) early. He walked the second batter of the game, Coco Crisp, to end his streak without issuing a walk at 24 1/3 innings. It's the longest streak of consecutive walkless innings by a rookie starter since San Diego's Josh Banks had a 25-inning streak in 2008. Beavan's 1.27 walks per nine innings are third lowest all-time by a rookie pitcher.
That was the beginning of Beavan's troubles. Crisp stole second, his 49th. That tied him with New York's Brett Gardner for the league lead.
Hideki Matsui singled to right and Willingham followed with his club-leading 29th, a three-run shot that caromed off the left-field, second-deck facade for a 3-0 lead.
With one game remaining, Willingham needs one home run for 30 and two RBI for 100.
"It would be really cool. That's one thing about baseball, you never know," Willingham said. "I'd be happy either way.
"That's not numbers I set before the season. I've always been a 20-25 home run guy and a 80 RBI guy. Fortunately, I've been healthy this year except for the 15 days on the DL (Achilles). That has allowed me to put up some numbers."
Willingham said Cahill "did a great job tonight. He ended the season exactly like he wanted to end the season. We saw a lot of the Cahill we saw in the first half when he was at his best."
Cahill's 40 career wins in his first three seasons are second most in Oakland history -- behind Vida Blue's 42 -- for a pitcher before his 24th birthday.
The A's pushed a couple more runs across in the third. Willingham drew a one-out walk and David DeJesus singled to left. Scott Sizemore singled to right, scoring Willingham and sending DeJesus to third.
DeJesus scored on Kurt Suzuki's sac-fly to deep left for a 5-0 lead.
Matsui opened the fifth with a single and eventually trotted home on Sizemore's two-out home run, his 11th, into the left-field bullpen.
Beavan gave up seven runs and eight hits in five innings.
It was the 11th shutout for the A's and the 15th time the Mariners have been shut out.
Melvin removed Crisp from the game in the ninth after a slight ankle twist.
"He was able to play but we were not in position there where we're going to run," Melvin said. "And I have an eye on the stolen base thing for him. I just got him out for an inning."
Willingham is one of 10 big-league players nominated Tuesday for the annual Hutch Award. The award, first given in 1965, is presented to the player who best exemplifies the honor, courage and dedication of player and manager Fred Hutchinson, who died of cancer at age 45. In his honor, his brother, Dr. Bill Hutchinson, founded the Fred Hutchinson Cancer Research Center in Seattle. ... With LH Jason Vargas nudging over the 200-inning mark (201) Monday, that gives the Mariners two 200-inning pitchers (Felix Hernandez has 233 2/3) for the first time since 2004 with Jamie Moyer (202) and Ryan Franklin (200 1/3). ... Mariners catcher Miguel Olivo will finish as the team leader in both home runs (19) and RBI (62), the first time ever for a catcher in Mariners history. He also will be just the fourth catcher to do that in the expansion era, since 1961. The others were: Cleveland's John Romano (1962), Detroit's Lance Parrish (1983, 1984) and Cleveland's Victor Martinez (2007).