Lance Berkman set up the inning by drawing a one-out walk, and Blum took a guess that he would see some fastballs. That prognostication turned out to be correct.
"Lance worked a pretty good walk in that situation," Blum said. "I was guessing with Lance's ability to steal a base and get into scoring position with one out, it might give me an opportunity to hit a fastball. I guessed right, and I just happened to get one to hit."
The win extended the Astros' winning streak to seven. It also marked their 73rd victory of the year, tying their win total from 2007.
To borrow one of baseball's most oft-used cliches, this one fit the bill of a proverbial "team win." The defense turned four double plays, the offense provided clutch hits and the pitching, with the exception of a hiccup or two along the way, held up long enough for the Astros to outlast the Cubs, thanks to Blum's career-high 14th homer of the year.
"That's what we've been doing lately -- we've been kind of getting it from everywhere and everybody," manager Cecil Cooper said. "Just contributions up and down the list."
The Astros broke open a 3-3 game with a four-run sixth, which started with Hunter Pence's leadoff triple off Bob Howry.
Humberto Quintero singled to short, and Reggie Abercrombie, pinch-hitting for Fernando Nieve, drew a walk to load the bases. As boos cascaded down from all corners of the ballpark, the infield scooted in for Michael Bourn, who singled up the middle, scoring two runs.
Michael Wuertz entered the game and walked Ty Wigginton, loading the bases for Miguel Tejada, who grounded into a double play, but Abercrombie scored from third to increase the Astros' lead to four.
The Cubs answered with two off Tim Byrdak in the bottom of the inning. Jim Edmonds drew a walk and advanced to third on Geovany Soto's double off the ivy in right, and Ryan Theriot drove them both in with a double down the right-field line. Chris Sampson coaxed groundouts from Reed Johnson and Alfonso Soriano, but Theriot snuck down to third on Soriano's out and trotted home when Mike Fontenot singled up the middle.
The Astros were ahead by a run until the seventh, when Edmonds knocked a solo homer off Doug Brocail to tie the game at 7. Wesley Wright stepped in in the ninth, walking the leadoff man before fielding a Mark DeRosa sacrifice bunt and firing to second to nab the lead runner. Wright struck out rookie Casey McGehee before ending the inning with a fly ball from the hot-hitting Soto.
Wright issued another leadoff walk, this one to Theriot, in the 10th. Kosuke Fukudome singled to left, but Wright retired the next three, recording fly-ball outs on Soriano and Henry Blanco before striking out Derrek Lee.
"The key was being aggressive," Wright said. "It was a situation where I hadn't been out there in a while, I felt fresh and I knew I had a pretty decent fastball coming out of the bullpen. I just wanted to be aggressive and let my defense and everybody else be involved, not try to record all the outs myself. I had to trust my stuff and go right at them."
Following Blum's home run, Cooper turned to his oft-used closer, Jose Valverde, to finish the game. Valverde, pitching for the fourth day in a row and the sixth time in seven days, struck out two in that inning and recorded his 39th save.
Cooper had planned to avoid pitching Valverde if at all possible. Turns out, apparently, it wasn't possible, at least not in Valverde's mind.
"We went down and talked to him a little bit," Cooper said. "He said, 'I want it.' I said, 'Hey, you've got to give it to him if he wants it.' I would have loved to have gone around him a little bit. We hoped that when we got the runs there early and got up by four, we said, 'Well, maybe there's a chance we can squeeze through it without having to use it.' It always seemed to come down to him. He gutted it out and did a good job for us again."
Both starting pitchers were out of the game by the end of the fifth inning. Cubs starter Carlos Zambrano left the game after five with arm soreness, and he is scheduled to be examined on Wednesday. Brandon Backe was lifted with one out in the fifth in favor of Nieve.