CHICAGO -- No one knew Carlos Zambrano was hurting.
The Chicago Cubs starting pitcher left after five innings on a hot and muggy Tuesday night, more than two hours before Geoff Blum won it for the Houston Astros with a two-run homer in the 11th inning.
Zambrano's short outing was almost forgotten after the Astros' wild 9-7 win.
So it was a bit of a surprise when Cubs manager Lou Piniella revealed that Zambrano left because of arm problems. Zambrano will have his right arm examined Wednesday.
Any absence could affect the Cubs, who are trying to hold on to first place in the NL Central, not to mention the best record in the league. With starter Rich Harden being skipped for precautionary reasons this week, this is news the Cubs didn't need to hear.
"He told our pitching coach he wasn't feeling good," Piniella said. "It has to be in his arm. I just don't know. We'll let you know tomorrow when we find out."
Blum's two-run homer off Kerry Wood sent the Astros to their seventh straight victory, one shy of their season high.
"That's what we've been doing lately," Astros manager Cecil Cooper said. "Getting it from everywhere and everybody. Just contributions up and down the lineup."
The first-place Cubs, who have lost four straight, all at home, remained 4½ games ahead of Milwaukee in the NL Central.
"We're in a stretch right now where things aren't going our way," Piniella said. "We've just got to battle through it. What can you do?"
Zambrano was coming off a poor August and was pushed back two days with arm fatigue. He didn't overpower the Astros, rarely hitting 90 mph, and gave up three runs, five hits and three walks in five innings. He was pulled after 86 pitches.
Zambrano was unavailable for comment, and his teammates were almost speechless about a possible injury.
"I had no idea," catcher Geovany Soto said. "I still don't know what's going on. To be honest with you, I think he was a little better than his last couple outings."
Wood (4-3) walked Lance Berkman and Blum sent the first pitch into the bleachers in right for his 14th homer. Wood struck out four in two innings.
"Lance worked a pretty big walk in that situation," Blum said. "I was guessing that with Lance's ability to steal a base and get into scoring position with one out, it might give me an opportunity to get a fastball. I guessed right."
The Cubs had 15 hits and eight walks, but they also hit into four double plays and stranded 12 runners. Third baseman Aramis Ramirez committed errors in the ninth, 10th and 11th innings.
"We squandered some opportunities, but we scored seven runs, which is ample enough to win," Piniella said. "Houston's playing well, give them credit."
Houston scored four runs in the sixth to take a 7-3 lead.
Miguel Tejada tied the game 3-3 with a two-run single off Zambrano, who didn't let on he wasn't feeling well. Bob Howry didn't have a lot of time before replacing Zambrano for the sixth and six batters later, he was booed off the field.
Hunter Pence started the carnage with a triple off the wall in center and David Newhan followed with a single. Humberto Quintero singled and Howry walked pinch-hitter Reggie Abercrombie. Michael Bourn hit a two-run single through a drawn-in infield, ending Howry's night, and the Astros scored one more on Tejada's double play grounder.
Houston is 7½ games behind Milwaukee in the wild-card race.
"We're going to keep believing and we're going to keep fighting every day," said Pence, who went 4-for-6, falling a homer shy of the cycle.
Jim Edmonds snapped a 1-for-14 slump with a solo homer in the seventh to tie it 7-7.
The Cubs had gone three games without an extra-base hit. Alfonso Soriano reversed that trend in the first with his fourth leadoff homer of the season, and the Cubs added three solo homers and three doubles.
"We had a very good offense today," Soriano said. "I hope we come back with more energy tomorrow."
Backe gave up the three solo homers in 4 1/3 innings. He allowed nine hits and walked two.
Slumping Cubs OF Kosuke Fukudome didn't start Tuesday, but entered as a pinch-hitter, walking once and getting a hit. He won't play Wednesday against lefty Randy Wolf, but the left-handed hitter should be back in the starting lineup this weekend, Piniella said. ... The Astros activated 2B Kaz Matsui from the 15-day DL, but he won't play until the weekend. Houston also brought up C J.R. Towles, RHP Alberto Arias and IF Edwin Maysonet. ... Cubs RHP Angel Guzman pitched for the first time since June 1, 2007, after undergoing Tommy John surgery. ... The Cubs set a club record, surpassing 3 million fans in 74 games, beating the previous record, set last year, by one game.