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DENVER -- Jeremy Guthrie walked off the field to a chorus of boos after a tough third inning and tipped his cap to the discouraged fans.

The weight of another poor outing from the Colorado Rockies starter had him venting at a disapproving crowd.

"Frustration, just frustration," he said of his cap gesture. "I understand where the boos come from, and like anybody else I was frustrated. Frustrated with myself. The fans didn't give up two home runs or six runs."

Staked to a four-run lead in the first inning, Guthrie came apart in the third in Colorado's 8-5 loss to the Oakland Athletics on Tuesday night.

The Rockies matched a season-high with their sixth straight loss, and Colorado fell to 0-7 in interleague games this season.

Guthrie (3-5) had his second straight short outing and he has struggled since returning from a strained right shoulder that landed him on the disabled list in late April. He is 1-4 since coming back, he has allowed 41 hits in his last four starts, and his ERA has risen to 6.91.

He allowed seven runs and eight hits, struck out five and walked two in five innings.

"I go in with a lot of confidence into each outing, unfortunately it hasn't worked out the last few," he said. "I believe I can get people out. It just hasn't happened."

Rockies starters came into the game with a 6.17 ERA and have consistently been out of the game before the end of the sixth inning.

"We need some people to pitch some good innings for us in the early part of the game," manager Jim Tracy said.

The Rockies gave Guthrie a cushion to work with after hitting Oakland starter Bartolo Colon hard in the first inning. Tyler Colvin began with a home run, his seventh of the season and fourth in three games, and Michael Cuddyer, Chris Nelson and Wil Nieves added run-scoring singles.

Guthrie couldn't make it stand up. He hit Jemile Weeks with a pitch to start the third inning and issued a one-out walk to Josh Reddick. Seth Smith and Brandon Inge hit successive doubles, and Brandon Moss followed with his first homer of the game, a two-run drive that smacked into a beer sign fronting the third deck. It was the first time this season and the 32nd time in the history of Coors Field that a homer reached the third deck.

Cliff Pennington closed out the A's big inning with a solo shot, driving Guthrie's first offering over the center field wall for his second homer of the season.

"A few bad pitches, a couple of which left the park," Tracy said. "We went from the position where we had to go from leading by four to playing catch-up. Day after day after day that gets to be somewhat daunting."

Todd Helton hit a solo homer in the fifth to cut it to 7-5.

The Rockies bullpen settled things down, allowing just three hits and one run, a solo homer from Inge in the seventh that made it 8-5. Colvin saved another homer when he reached over the center-field wall to rob Pennington in the eighth.

"Luckily he got under it just enough and me having enough time to get to it, and enough time to catch it," Colvin said. "I saw where the wall was, and once you feel where the track is you guesstimate when you need to jump."

The Rockies tried to rally in the ninth. Ryan Cook walked Colvin and gave up a single to Marco Scutaro before striking out Carlos Gonzalez and Cuddyer. He then got Helton to bounce into a game-ending fielder's choice for his first career save in two chances.

Game notes

Colvin's homer to lead off the game marked the second time the Rockies have done it this year. Dexter Fowler did it on May 28. ... The Rockies swept a three-game series in Oakland the last time the teams played in 2009. ... Athletics RHP Brandon McCarthy was scratched from his scheduled start Wednesday. The A's moved up LHP Tommy Milone (6-5) in the rotation to take over for McCarthy. He will face Rockies right-hander Alex White (2-4). ... The Rockies traded RHP Esmil Rogers to the Cleveland Indians for cash considerations after designating him for assignment last week following the signing of LHP Jeff Francis.