PHOENIX -- The Oakland Athletics are in the wrong division.
Fresh off a three-game sweep of Bay Area rival San Francisco, the Athletics came into the desert and blew out the stumbling NL West leaders. Eric Chavez, Kurt Suzuki, Bobby Crosby and Rajai Davis also homered for Oakland, which improved to 6-1 all-time at Chase Field.
Ellis doubled in the first and hit a solo homer in the second against Webb, and he added a three-run shot in the ninth against Arizona closer Brandon Lyon.
"Tonight felt good," said Ellis, whose four RBI were one shy of a career high. "It's a nice ballpark to hit in. The ball carries real well."
The Athletics hit so many homers that manager Bob Geren lost count.
"Our offense was our best performance of the year," Geren said. "We had five homers, five doubles, eight or nine walks. It's obviously a good recipe to score runs."
The game had a distressing familiarity for the NL West-leading Diamondbacks, who have been outscored by a combined 35-7 during a three-game skid.
"You can put away a bad loss," manager Bob Melvin said. "Three of them is obviously a bit of a concern. We haven't played well three days in a row, offensively or on the pitching end."
For all their woes, the Diamondbacks remain 4 1/2 games ahead of Los Angeles in the feeble NL West. Arizona is 7-14 since May 26 but have added a game to its lead in that span.
Justin Duchscherer (7-4) went eight sharp innings, allowing one run and five hits while striking out six.
Four A's -- Ellis, Chavez, Crosby and Ryan Sweeney -- were halfway to the cycle by the fourth inning.
"Obviously, it's a great day for our offense, and to do it against a pitcher of that caliber makes it even more special," Geren said.
Webb (11-3) lasted 3 1/3 innings, his shortest outing since Sept. 17, 2004, when he went two innings at St. Louis. He allowed a season-high seven earned runs and nine hits. He struck out three and walked five.
Oakland teed off on the 2006 NL Cy Young Award winner, who is 2-3 since winning his first nine starts.
Ellis led off the game with a double and scored on Chavez' 6-4-3 double play, and Crosby's two-out double made it 2-0.
The A's added another run in the second on Ellis' homer, his seventh, and made it 4-0 in the third on Carlos Gonzalez' groundout.
In the fourth, Chavez hit a two-run shot to give Oakland a 7-0 lead and chase Webb, who left without speaking to reporters.
Melvin said Webb looked good in the bullpen, but his stuff didn't carry over to the game.
"He came out of the bullpen feeling great," Melvin said. "You've got to give them credit. They hit some good pitches."
Suzuki homered in the fifth off reliever Edgar Gonzalez.
Crosby led off the ninth with a home run off Lyon, and Ellis went deep two outs later. Davis hit Oakland's sixth homer against Doug Slaten.
The barrage provided plenty of support for Duchscherer, who has won four of his last five starts.
Duchscherer breezed through the light-hitting Diamondbacks, who entered with a .248 batting average, 12th in the NL. He retired 10 of the first 11 men he faced and didn't give up a run until the fifth, when Mark Reynolds doubled and scored on Edgar Gonzalez' groundout.
"Early, we scored some runs and it gave me a little bit of a cushion, where I felt like I could go out there and really pound the strike zone and let my defense do its job," Duchscherer said.
Duchscherer had a tense moment in the second, when he swung and felt a twinge in his surgically repaired hip. Geren and a trainer visited him, and Geren ordered Duchscherer not to swing the rest of the game. Duchscherer went down looking four times.
"That's why I looked so bad up there," Duchscherer said.
- Arizona LF Eric Byrnes, out since May 27 with injuries to both hamstrings, will go on a minor league rehab assignment this weekend and is expected to rejoin the club in Boston Monday.
- Ellis' homer snapped a six-game homerless streak for the A's, their longest since they went nine straight without a homer from Sept. 14-24, 1983.
- Arizona RHP Dan Haren faces his former team on Wednesday night. The Diamondbacks acquired Haren from Oakland in an eight-player deal that sent CF Carlos Gonzalez, LHP Dana Eveland and LHP Greg Smith to Oakland. Gonzalez robbed Arizona SS Stephen Drew of extra bases with a leaping catch at the wall in the eighth.