The D-backs entered the series with a one-game lead on the Rockies, but left three games behind with six to play.
"They came out ready to play," D-backs Sunday starter Wade Miley said. "I guess we had a battle in the trenches for the last-place team, I guess, and they really didn't really want to be there and they took care of that."
It was the first-ever four-game sweep for the Rockies over the D-backs and Colorado outscored Arizona, 35-13, in the series.
"I don't really have an explanation for you," D-backs manager Kirk Gibson said. "We tried to throw everything at them. They swung the bats really well, scored a lot of runs and we didn't, we weren't swinging the bats real well and we weren't able to shut them down."
Only the Rangers entered Sunday with a worse record than the D-backs. Arizona must win at least one of its remaining six games to avoid losing 100 games for the second time in franchise history.
"Nobody wants to have the worst record," Miley said. "We've just got to put today behind us and move forward and just grind out the rest of the year and see what happens."
The trouble started early for Miley (8-12) with the Rockies scoring a run off him in the second on DJ LeMahieu's RBI single and two more in the third on a two-run double by Brandon Barnes.
The Rockies chased Miley from the game in the fifth as Gibson had seen enough from the left-hander and removed him with one out, one run in and the bases loaded.
"Didn't have very good command at all," Miley said. "And it's getting old to have one good start and then the next start where you walk three or four guys. Couldn't find the fastball early and it just snowballed with every other pitch."
Reliever Randall Delgado promptly gave up a two-run double to Rafael Ynoa as the Rockies went up, 6-0.
Colorado starter Christian Bergman (3-4) kept the D-backs off the board through the first five innings.
The D-backs were finally able to get something going against him in the sixth when Mark Trumbo hit a two-run homer, his 10th of the year. Trumbo also hit a solo shot in the ninth.
"Ultimately, it's not a good day, but for me personally it was a step in the right direction," Trumbo said.
Trumbo has worked to hit the ball in the air more lately, altering both his approach and mechanics at the plate to do so.
"I've been working on some things," Trumbo said. "At times they're showing up, at times they're not. But today they worked out. There's no money for me on the ground. I need to drive the ball. I need to hit the ball in the air. It's frustrating when you're not doing it, but fortunately today I was able to get a few out there and that's kind of what I need to do."
Still that was a rare bright spot for a team struggling to finish the season without a complete collapse.
"It's miserable," Trumbo said. "There are a few positives here and there but ultimately it's been pretty lousy. We've got six games left. Give it everything you've got."