Carlos Gonzalez hit his 20th homer off Dempster and added an RBI single and Ian Stewart and Troy Tulowitzki each drove in three runs to spark the Rockies, who led 5-2 going into the eighth.
The last time the Cubs gave up 17 runs was July 3, 1999, at Philadelphia, when the Phillies totaled 21. The last time they gave up 21 hits was that same game. The last time they gave up 12 in one inning was Sept. 24, 1985, against Montreal, top of the fifth, when they also served up a dozen.
Sean Marshall, who had given up one earned run over 14 1/3 innings in July, started the eighth for Chicago. Clint Barmes doubled and pinch-hitter Melvin Mora singled, but Marshall struck out the next two batters and had two strikes on Gonzalez. He singled to drive in Barmes. That was hit No. 1 of the 11 straight, which included a two-run double by Brad Hawpe, a two-run homer by Stewart, and a two-run homer by Dexter Fowler.
In his second at-bat of the inning, Tulowitzki hit his second double, driving in two more, and then Hawpe walked to end the streak.
"Tomorrow, if you brought out [Aramis] Ramirez and [Derrek Lee] and Marlon Byrd and let them throw [batting practice] and put nine fielders out there, I have a tough time thinking they could get 11 straight hits," Dempster said. "That's how crazy that is. That's how really remarkable it is.
"They weren't hitting pitches down the middle -- they were hitting pitches off the ground, they were hitting pitches inside, outside, everywhere," he said. "You tip your cap to them, but it's embarrassing. You don't want to go through stuff like that."
Marshall gave up five runs on five hits over two-thirds of an inning. Andrew Cashner couldn't retire any of the six batters he faced, giving up hits to each of them. They all scored. Brian Schlitter was charged with the final three hits of the streak and also walked two before getting Stewart to fly out to center and end the infamous inning.
"Usually in a Little League game you see that, but never in a big league game," Fowler said. "It's crazy."
"That last inning, I've never seen an inning like that," Cubs manager Lou Piniella said. "We had two outs and two strikes on the hitter [Gonzalez] and they scored 12 runs. I've never seen anything like that.
"I feel bad for my pitchers," he said. "I feel bad for the young kids trying to get the job done and they get in trouble and don't have the answers on how to get out of it."
What now? In his past two outings, Cashner has given up 12 runs on eight hits over 1 1/3 innings.
"I think the easiest thing we can do is for me to come back in and do my work like I always do and [Cashner] sees that and sees that it's OK," Dempster said. "You're going to have tough outings. You just have to go back out there. What's the worst that can happen? You lose? I've done that before.
"Don't change anything, just keep preparing and doing your job and things will turn," he said. "[Cashner] has tremendous stuff. It was one of those crazy nights. You have to somehow let it go when you leave here because we have to come back and win a game tomorrow."
This will be a tough one for Dempster (8-8) to shake off, too. It was the shortest outing of the season for the right-hander, who was charged with five runs on eight hits and five walks over four-plus innings. The last time he didn't get past the fifth was May 25, 2009, against the Pirates when he gave up six runs over four innings.
"His command was off," Piniella said.
Dempster said he began the game with an aggressive approach, but then Rockies starter Jeff Francis singled with one out in the third and suddenly he was "unaggressive." Fowler doubled and both he and Francis scored on Seth Smith's double. One out later, Dempster walked three straight batters to force in another run and give the Rockies a 3-0 lead.
"I'd rather take the 11 straight hits than go and do that and I mean that," Dempster said of the walks. "You have to attack guys and go after them, especially in this ballpark. Walks will hurt you. It's a pretty easy formula -- you keep guys off base and you'll have more success."
Dempster also served up Gonzalez's 20th home run, which was the 20th off the Cubs right-hander in 144 2/3 innings. Last year, Dempster served up 22 in 200 innings.
The Cubs collected four hits. Total. That's how many hits Gonzalez finished with.
"That was a crazy inning," Marshall said of the eighth. "I don't think an inning like that will ever happen again."
All Piniella could do was shake his head in disbelief.
"I've never seen that," he said. "Never seen it."