Chicago hadn't dropped four straight since June 26-29. It also snapped an 11-series winning streak.
The long-time leaders of the National League are appearing beatable for the first time in months. It might come as a shock to many Cubs fans, but not to manager Lou Piniella.
"Did anybody think this was going to be real easy?" Piniella said. "You didn't hear that from me all year, have you? We're in a stretch now where things aren't going our way. We've got to keep playing and keep battling and keep our confidence, and that's it."
The team also lost ace Carlos Zambrano, who came into the start battling arm fatigue and took himself out after five innings of three-run ball because of arm soreness. He gave up five hits, walked three and struck out three on 86 pitches in his first start in a week, leaving with a 3-3 tie.
Zambrano will be examined by a doctor on Wednesday, and the club didn't have details on the injury. Losing the ace would be a huge blow to a team already reeling with a nine-game road trip looming.
"That's the biggest news of the night, because we don't know how he's feeling," left fielder Alfonso Soriano said. "I hope everything is good, because he's very important for the team."
Solo homers by Soriano, Mark DeRosa, Geovany Soto and Jim Edmonds revived a flat-lining lineup, but the momentum appeared to die when Bob Howry gave up four runs without recording an out in the sixth. The Cubs answered with four runs over the sixth and seventh to tie it, but could not come through in scoring situations in the final innings.
Fortunately for the suddenly cooled Cubs, the second-place Milwaukee Brewers lost in extras, too. Chicago kept a 4 1/2-game cushion in the National League Central, though that lead could be whittled down if this keeps up.
"Right now, the key is for us to get back on track and to start winning ballgames," Howry said. "We've got to get it straightened out and start winning. That way, we don't have to worry about what [the Brewers] do."
They did their best to get it straightened out on Tuesday. Down 7-3, the Cubs plated three in their sixth on doubles by Soto and Ryan Theriot and a Mike Fontenot RBI single. Edmonds' 17th homer completed the comeback and tied it in the seventh.
The Cubs loaded the bases with one out in the eighth, only to have Derrek Lee ground into his 25th double play, second-most in the NL to the Astros' Miguel Tejada. The leadoff man walked in the ninth and 10th, but Houston escaped both times.
"We squandered some opportunities, but we scored seven runs, which is ample enough to win," Piniella said of his team, which grounded into four double plays on the night. "We didn't do it today. Houston's playing well, give them credit."
Soriano's fourth leadoff homer of the season and 48th of his career jump-started the slumping offense. It marked the club's first extra-base hit since Soriano's game-winning home run on Friday. He leads active players in career leadoff homers and ranks third all-time behind Rickey Henderson (81) and Craig Biggio (53).
DeRosa led off the fourth by going deep to left, and Soto, who fell a triple shy of a cycle, homered to center one out later. Both picked up their 80th RBIs.
Howry replaced Zambrano in the sixth and gave up four hits and a walk before getting pulled. Michael Bourn's back-breaking two-run single made it 6-3 and chased the right-hander. Michael Wuertz came in and gave up the final run of the inning -- charged to Howry -- on a double play.
Howry's line was especially disappointing considering the progress he made against the Phillies last weekend, throwing four scoreless innings and striking out four. He hoped he had broken out of his second-half slump.
"It was frustrating," Howry said. "I went out and threw three times in the Philadelphia series, threw the ball well, feeling pretty good. I wanted to come out and do really good tonight. I didn't locate pitches."
Casey McGehee made his Major League debut with a pinch-hit strikeout, and reliever Angel Guzman tossed a scoreless inning in his first big league appearance since June 1, 2007, after coming back from Tommy John elbow ligament replacement surgery.
But it was hard to dwell on positives on this night.
"Four in a row, we've got to get it fixed," Lee said. "It's not the right time of year to be going in a skid. They happen, but we've got to get it turned around."
Nick Zaccardi is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.