It was perfect timing. With the game tied at 1, Chris Sampson (4-2) walked Derrek Lee, who went to third on Aramis Ramirez's single. Milton Bradley was intentionally walked to load the bases for Soriano, who drove a 1-0 pitch to straightaway center for the game-winner.
"He's been consistent lately," Cubs manager Lou Piniella said of Soriano, who has accepted the switch from leadoff man to No. 6 hitter. "He's been hitting the ball for some power and with men on base, which is what you want to see. He's been streaky, there's no question, I think he admits that himself, but right now he's streaky in the right direction."
The Cubs have won 11 of their past 14 games, and with the win matched their season high of seven games over .500. Second-place St. Louis kept pace by beating the Los Angeles Dodgers, 6-1, on Monday.
"We don't think about being in first place," said Carlos Zambrano, who started the game and went seven innings. "We still have to do our job to keep our team in first place. We have to keep playing the way we're playing in the second half, every game, game by game, and that's it."
The Cubs had chances earlier. They loaded the bases with one out in the ninth, but Bradley was tagged out on a botched suicide squeeze attempt as Mike Fontenot, in a pinch-hit at-bat, missed the bunt.
"It was a squeeze, and I didn't hit the ball," Fontenot said. "We did have the squeeze play on. Fastball, 97 [mph], and I didn't get the barrel on it."
Was he surprised at the play?
"I don't know -- we've done it in the past," Fontenot said. "I just didn't get it down. The good thing is we won the ballgame."
"It was a good pitch to bunt," Piniella said. "The ball was a little on the outside part of the plate, but you've got to at least foul the ball off. Anyway, forget the squeeze. We won the ballgame and we used a lot of pitching, but it was worth it."
Young pitchers Jeff Stevens and Jeff Samardzija, who got the win in relief, deserve a lot of credit. Stevens did give up a two-out triple to pinch-hitter Jason Michaels in the 10th, but rebounded to fan Ivan Rodriguez, stranding Michaels while striking out the side.
"I was just trying to throw strikes and keep us in it," Stevens said. "I was focused on the plate and the glove, and that's all I was conscious of what was going on.
"Everyone's throwing great, it's a 1-1 game, and you don't want to be the guy who ... doesn't do their job."
The Cubs survived another mini-gaffe in the 11th. With one on and one out, Soriano thought he'd fouled a ball off his foot and stayed in the batter's box. But it was ruled fair, and he was easily thrown out.
"I thought it was a foul ball, so I didn't think to run to first base because it hit me on the foot," Soriano said.
Others who contributed included rookie Jake Fox, who was needed to back up Koyie Hill. This was Hill's 17th consecutive game behind the plate, subbing for injured Geovany Soto. The last Cubs catcher to do that was Rick Wilkins in 1991. Fox, who entered in the 10th, made a great stop of a fastball that got away from Samardzija.
"What a nice job," Piniella said of the rookie. "The ball Samardzija threw before the double play ball [to end the 13th], that's a real athletic play for a catcher. I thought he did a wonderful job."
The two opposing Lees exchanged home runs early. Carlos Lee led off the Houston second with his 16th homer, connecting off Zambrano, who gave up three hits.
"Everything was working, except for that pitch to Carlos Lee," Zambrano said. "I think he's got my number. He's a good hitter, and next time I should walk him."
Derrek Lee, who hit 20 homers total in 2008, notched his 20th of '09 leading off the Chicago fourth when he sent an 0-2 pitch from Astros starter Wandy Rodriguez over the left-field bleachers and onto Waveland Avenue. It's the sixth time the two Lees, who are not related, homered in the same game.
The game stayed tied until Soriano's heroics in the 13th. His family was sitting in the front row at Wrigley, watching and cheering.
"We got what we wanted by stretching out 'Z' and getting him out of the game," Astros manager Cecil Cooper said, "but they went to the 'pen and just outlasted us. It's just unfortunate we didn't get a big hit when we needed one."
Nope. But Soriano did.