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PHOENIX -- Not even Ubaldo Jimenez could escape the Colorado Rockies' ill-timed funk.

Jimenez allowed two home runs in a game for the first time since June 6, 2008, and the Arizona Diamondbacks sent the Rockies to their third straight loss, 8-4 on Wednesday night.

"He was not himself tonight, that's all," manager Jim Tracy said of Jimenez. "He could not get into any kind of rhythm whatsoever. He was mechanically out of whack."

Stephen Drew led off the first inning with a homer and Adam LaRoche added a two-run shot in the third. Chris Young's two-run single put Arizona up 5-4, then the Diamondbacks added three in the eighth, two on Kelly Johnson's home run.

Jimenez (19-7) lasted just four innings, giving up five runs and six hits. He couldn't hold a 4-0 lead Colorado gave him in the first on Melvin Mora's three-run homer and Todd Helton's solo shot.

"With your best pitcher on the mound you expect to win the game," Mora said, "but I guess it's one of the games he doesn't feel the command of the ball. That was hard to believe that happened."

Jimenez hit 100 mph on the ballpark radar gun, and that was not necessarily a good thing, he said.

"I probably felt too good with my arm, my velocity. That's what probably got me into trouble," Jimenez said. "It felt so good that everything was too much. I was flying open. I couldn't locate my fastball or throw my fastball down."

The Rockies lost a half-game in the NL West race, falling three behind first-place San Diego.

Colorado sends Jeff Francis to the mound Thursday night to try to prevent a three-game sweep by the last-place Diamondbacks. Tracy did not try to hide the significance of that contest, with the Rockies headed home for three against San Francisco starting on Friday.

"We need to take a major step forward tomorrow night because you certainly wouldn't feel too good about yourselves from a momentum standpoint going home after getting swept here, that's for sure," Tracy said. "Tomorrow's a very, very big game for us."

Rodrigo Lopez (7-14) retired 13 of the last 14 Colorado hitters he faced. Four relievers held the Rockies scoreless over the final four innings.

Sam Demel pitched 1 2/3 innings to get his second save in two tries.

Arizona interim manager Kirk Gibson, still waiting to find out if he will return next season following the hiring Wednesday of general manager Kevin Towers, said he doesn't like for his team to be considered a spoiler. He said he just wants his team to "push hard to the last out of the last game this year," especially with Arizona just coming off a sweep at the hands of the Pirates in Pittsburgh.

"We have been frustrated for sure but to come back and play this way against Colorado, against Ubaldo tonight, being down four runs in the first inning is a credit to their determination," Gibson said.

Jimenez fell to 4-6 in 13 starts since beginning the season 15-1. The Rockies are 3-5 after winning 10 straight.

Mora, batting over .300 since replacing the injured Ian Stewart at third base 20 games ago, hit Lopez's full-count pitch onto the concourse in deep left field, where a fan caught it. Helton followed with a solo homer to make it 4-0 in a hurry.

Drew led off the Arizona first with an opposite-field line drive over the fence in left field to cut it to 4-1.

The Diamondbacks scored two in the third and two in the fourth.

LaRoche's 24th home run of the season brought home two runs in the third to cut the lead to 4-3.

The Colorado ace almost escaped the fourth-inning jam after Brandon Allen drew a leadoff walk and Gerardo Parra beat out a bunt single. Lopez squared for the anticipated sacrifice bunt, then brought the bat back and swung away, grounding into a double play.

But Drew walked on four pitches and stole second, then Young looped a single to left. Ryan Spilborghs bobbled the ball briefly as Allen and Drew scored on what was ruled a two-run single.

Game notes

Jimenez had given up one home run in his previous 11 starts, none in his last five. ... LaRoche increased his career-best RBI total to 95. ... Tracy said Jason Hammel will be on a short leash when he starts against San Francisco on Saturday. Hammel was lifted in the fourth inning Sunday against Los Angeles because of a tired arm. ... The Rockies fell to 31-45 on the road. ... The Diamondbacks fanned 14 times one night after breaking the major league season strikeout record.