CHICAGO -- The Houston Astros had a golden opportunity to bolt from Chicago with two wins against the best team in the National League. Instead, they were pummeled in the finale at Wrigley Field.

It didn't take long for Brandon Backe to relinquish a comfortable lead his teammates built against Cubs No. 5 starter Jason Marquis and turn it into a landslide defeat, allowing eight runs in the third frame in an 11-4 loss before a packed house on Wednesday afternoon.

"I just got hit around, that's all there is to it," Backe said. "It just wasn't a good day out there today. Regardless of what was going on, I just didn't get the job done. I left some pitches up in the zone, and they took care of it."

Backe had two outs in the third when he issued consecutive walks to Aramis Ramirez and Jim Edmonds to load the bases, and from there, the floodgates opened. Mark DeRosa launched a grand slam to left, Kosuke Fukudome doubled to right, and after Backe intentionally walked Geovany Soto, starting pitcher Jason Marquis doubled Soto home.

Alfonso Soriano capped the eight-run inning with a three-run homer.

"You just can't do that," Backe said of the rally-igniting walks. "Close pitches just missed, and it put me in a bad situation to ultimately give up the big hit after that. The walks got me to the situation where I couldn't make a mistake, and I did."

Manager Cecil Cooper felt Backe was being squeezed by home-plate umpire Marty Foster in the second inning and wondered if that contributed to Backe's struggles in the third. Backe declined to delve into that line of questioning, however, opting instead to attribute the loss simply to bad pitching on his part.

"If I say anything about [the umpires], it just digs a deeper hole for me," Backe said. "I'm just going to go ahead and say it was all my fault. It's tough to pitch in the zone and get people out constantly. You have to somehow get them to fish for something outside the zone, and I just couldn't do that today.

"Anything that was falling off the plate, they didn't swing at, and anything that was up in the zone, over the plate, they pretty much hit. It just was a bad day for me."

The most recent Astros starting pitcher to give up as many as 11 earned runs in a start was Jason Jennings on July 29, 2007, vs. the Padres. He allowed 11 runs in two-thirds of an inning.

As Backe suffered through the third, the bullpen stayed put. The Astros started the game short two relievers, with Geoff Geary -- who's battling a sore groin -- and Chris Sampson unavailable. That meant Backe was going to have to go deep into this game. Pitch-wise, he did. By the time Cooper mercifully yanked him with one out in the fourth, Backe had thrown 99 pitches.

Backe was more upset that he didn't contribute more innings than he was about allowing double-digit runs. He recalled lecturing Wandy Rodriguez about this very subject, having told the left-hander on Tuesday to put the first two bad innings behind him and focus on giving the Astros a full day's work.

But the next day, Backe was unable to practice what he preached.

"I had constantly told Wandy yesterday, 'It's a new game, try to get us into the sixth and you've done your job from here on out,'" Backe said. "I pretty much told myself the same thing internally, just do what I told Wandy, because our bullpen has really taken a brunt this whole year."

Noting the Astros are in the midst of a stretch of 33 games in 34 days, Backe berated himself for his role in taxing the 'pen even more. He also praised Tim Byrdak, who didn't allow a run over 3 2/3 innings in relief.

"You just can't have games like this, and Byrdak really stepped up today," Backe said. "He can't get enough praise for what he did today, just backing me up and backing the whole pitching staff together. He gets all the credit, and I should get all the blunder, I guess."

Earlier, the Astros appeared primed to win their fourth series in a row after they built a 4-1 lead against Marquis. Lance Berkman drove in the first run with a base hit to right, scoring Kazuo Matsui, and Carlos Lee cleared the bases with his 27th home run of the season.

Before their Chicago trip, the Astros hadn't lost a series since they were swept by the Pirates at home July 21-23.

"You look at this series, and you get [Ryan] Dempster and [Rich] Harden and Marquis, and those are three pretty tough right-handed pitchers, and we have a predominantly right-handed lineup," Berkman said. "We could have swept the series, but we certainly could have won two out of three, and it just didn't happen.

"We didn't make the pitches when we needed to make them. Sometimes that happens, and we just have to try to rebound from it and move onto the next series."