"The miscue that we made in the third inning, a very makeable play and more than likely a double play," manager Jim Tracy said.
The Rockies led 3-0 thanks to Seth Smith's three-run homer in the first when Jimenez gave up an infield single to pitcher Rubby De La Rosa to start the third.
Jamey Carroll followed with a bouncer to third base, a ball that was chest-high and seemingly an easy play for Wigginton, but bounced off his glove for his second error in two games.
Aaron Miles bunted into a fielder's choice and De La Rosa was thrown out at third. Jimenez struck out Andre Ethier, pitched carefully and walked Matt Kemp but gave up a first-pitch grand slam to Loney.
"Two out with nobody on with Aaron Miles (batting), it turns into a five-run inning," Tracy said. "A situation where you got to go through Ethier, you pitch around Kemp and Loney ends up hitting a grand slam."
Jimenez (1-7) ended up throwing 22 pitches after Wigginton's error and gave up three straight singles and a fifth run in the inning before getting De La Rosa (3-0) to ground out to end it.
The Rockies scored 15 runs on 24 hits in the final two games of the series but lost both, ending up with a split of the four-game series.
"It's painful knowing that we could have won the whole series, every game," said Carlos Gonzalez, who went 3 for 5 and hit a two-run homer in a four-run seventh. "We couldn't just hold them (from) scoring runs. It's difficult to win that way."
Wigginton was not available after the game.
Jimenez had allowed four homers in 66 2-3 innings in his previous 11 starts and none in 37 innings in his past five.
He gave up solo homers to Kemp and Rod Barajas in the fifth and left after allowing seven runs, two earned, and 11 hits in 5 2-3 innings. But Tracy watched his offense come back from a 9-3 deficit, get within two runs thanks to the four-run seventh that included two-run homers by Gonzalez and Troy Tulowitzki, and wondered again about the fateful third.
"I don't know how well Ubaldo would have done today," Tracy said. "My gut tells me he might have pitched us right to the back end of our pen. You can't ask them to do much more offensively than they did today and they've done the last five days. You have to catch the ball and in catching the ball, you don't allow additional hitters to come to the plate that otherwise wouldn't be walking up there."
Jimenez gave up three homers in a game for the first time in his career. He had given up two homers five times, including April 1 in his opening day assignment against the Diamondbacks.
"As a pitcher, every time that happens, you just want to go back and make pitches and try to pick your team up," Jimenez said. "I tried to do everything within my means. It just didn't happen."
Loney's grand slam was the second of his career. Both have been at Coors Field. He hit a split-finger pitch, driving it just over the scoreboard in right field, much to Jimenez's surprise.
"It didn't dive but to tell you the truth, I don't think he hit it that good," Jimenez said. "He was like kind of in front of it. I thought it was a fly ball to right field and it just carried and carried."
The Rockies have won one of Jimenez's 12 starts this season. He's 1-2 with a 2.06 ERA in five road starts. But at Coors Field, Jimenez is 0-5 with a 7.05 ERA.
"I guess he's not feeling really well pitching here," Gonzalez said. "From what I see, his velocity's been different. When he was pitching on the road, he was throwing a lot harder. He was throwing like 97 or 98. And I didn't see that pitch today. Maybe that's been the difference."
Notes: Loney's other grand slam came Sept. 28, 2006, at Coors Field, when he had a career-high nine RBI. ... Jimenez allowed 11 hits, one shy of the season-high 12 he gave up May 27 in six innings against the Cardinals. ... Jason Hammel is expected to make his next start Friday against the Tigers. He left the game Saturday night in the sixth inning after his lower back tightened up. Hammel said his back was still somewhat sore but he expected to make his start.