The first-place Cubs, who have lost four straight games, all at home, remained 4½ games ahead of the Milwaukee Brewers in the National League’s Central Division.
Wood (4-3) walked Lance Berkman and Blum sent the next pitch into the right-field bleachers for his 14th homer.
The Cubs had 15 hits and eight walks, but they also hit into four double plays and stranded 13 runners. Third baseman Aramis Ramirez committed errors in the ninth, 10th and 11th innings.
Wesley Wright (4-3) pitched two scoreless innings and Jose Valverde worked the 11th for his 39th save, ending a game that took 4 hours, 17 minutes in stifling, humid conditions.
Derrek Lee hit into a costly double play in the bottom of the eighth after Doug Brocail walked the bases loaded with one out. Lee hit a grounder to third and couldn’t beat the throw from second. Lee also struck out with two on and two outs to end the 10th.
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 a rested but underwhelming Carlos Zambrano. Bob Howry replaced Zambrano in 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.
The Cubs scratched back in the bottom of the inning, cutting the Astros’ lead to 7-6. Ryan Theriot hit a two-run double and scored from third on Mike Fontenot’s single. Jim Edmonds snapped a 1-for-14 slump with a solo homer in the seventh to tie it 7-7.
Chicago took a 3-1 lead in the fourth on homers by Mark DeRosa and Geovany Soto off Brandon Backe.
Alfonso Soriano hit his fourth leadoff homer of the season, and the Cubs added three more solo homers and three doubles, but it wasn’t enough.
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.
