"The guys battled hard and played hard," Astros manager Cecil Cooper said. "We had some chances and just didn't get the big base hit. We got what we wanted by stretching out [Cubs starter Carlos Zambrano] and getting him out of the game, but they went to the 'pen and just outlasted us. I thought all the guys threw the ball well. It was just unfortunate we didn't get a big hit when we needed one."
Zambrano and Astros starter Wandy Rodriguez each gave up only a solo homer in seven innings -- Carlos Lee homered off Zambrano in the second and Derrek Lee off Rodriguez in the fourth -- before each team's bullpen tightened the screws.
Five Cubs relievers combined to throw six scoreless innings, even though the Astros had at least one runner reach base from the ninth through 13th innings. Houston got a leadoff single from Michael Bourn in the 13th but couldn't get him home. Bourn went to second on a sac bunt, Tejada walked and Carlos Lee hit into an inning-ending double play.
"I got the two best hitters on my club coming next, and somebody's got to drive in a run," Cooper said when asked if he thought about stealing second with Bourn prior to the sacrifice.
Sampson, who was pitching for the first time since July 10, threw a perfect 12th before running into trouble in the 13th. He walked Lee on four pitches, gave up a single to Aramis Ramirez and intentionally walked Milton Bradley to load the bases.
With the outfield playing extremely shallow, Soriano crushed a 1-0 pitch and sent it high into center field. The only question was where it would land, and it cleared the fence for the first walk-off grand slam by a Cubs player in nearly 16 years.
"I just wanted to try to put the ball in the air and score a run," Soriano said. "I made a very good swing. That's the best swing I made in the second half."
Sampson was understandably upset after the game and didn't offer up any excuses, despite pitching for the first time in 17 days.
"I still have to go out and make pitches -- and didn't do it," he said.
The Astros used four relievers, with Jose Valverde pitching out of a bases-loaded jam in the ninth inning after the Cubs flubbed a squeeze attempt. Valverde entered the game in the eighth after LaTroy Hawkins was ejected for arguing balls and strikes.
Alberto Arias threw two scoreless innings before giving way to Sampson (4-2), who came off the disabled list Sunday. Cooper had said he didn't want to use Sampson in pressure situations right away, but he said he had no choice.
"Almost out of necessity really," he said. "Jeff [Fulchino] threw yesterday, and I wanted to kind of use my lefties in situational [roles], and Wesley [Wright] threw yesterday, so we were kind of stuck in some ways. You hate to do that with a guy just off the DL.
"I thought he threw OK in the first inning and kept it down, and then command became an issue in the second. He's been in a lot of big moments for us, and there will be a night when he will bounce back. I'm sure it hurts, but he will bounce back."
Carlos Lee crushed an 0-2 pitch to lead off the second inning and sent the ball over the wall in straightaway center field to give the Astros a 1-0 lead. It was the 297th career homer for Lee, leaving him three shy of becoming the third Houston player to reach 300 this season.
"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 answered for the Cubs in the fourth, hitting an 0-2 pitch from Rodriguez down over the left-field bleachers and out of the ballpark to tie the game at 1. Rodriguez didn't get a decision, but finished July with a 4-0 record and 0.75 ERA
"Wandy pitched really good," Cooper said. "I didn't think he was particularly sharp, but I thought he battled and kept us in the game and matched [Zambrano] pitch for pitch. You can't ask for much more than that."