• Unsung hero: Matt Murton blasted a pinch-hit home run in the seventh to pull the Cubs within a run.
• Hunt for October: The Cubs maintained their 1½ game lead over the Brewers in the NL Central.
• Quotable: "What a huge win. That's our biggest of the year. Clutch, clutch by Mr. Lee." -- Cubs manager Lou Piniella
-- ESPN.com news services
Cubs 6, Astros 5
CHICAGO (AP) -- Before Derrek Lee even had a chance to look at the big, old-fashioned scoreboard at Wrigley Field, a helpful Cubs fan let him know what he needed to do.
Trailing 5-4 and with the Brewers and Cardinals already in the win column, Alfonso Soriano singled off Astros reliever Chad Qualls (6-4) and with two outs, Lee homered on an 0-1 pitch to left-center field to cap a four-run comeback by the Cubs.
"Actually a fan yelled at me and told me Milwaukee and St. Louis had won. So I was aware of it," said Lee, who came out of the dugout for a curtain call after his home run. "At this point in time, you don't want to lose games in the standings and you don't want to lose series."
Carlos Marmol (5-1) got one out in the eighth inning and Ryan Dempster pitched a perfect ninth for his 25th save for the Cubs, who remained 1½ games ahead of the Milwaukee Brewers in the division. Cubs Center fielder Jacque Jones also made a diving catch with two outs on Mark Loretta's drive to left-center with a runner on second in the eighth inning
"What a huge win," said Cubs manager Lou Piniella. "That's our biggest of the year. Clutch, clutch by Mr. Lee. We talked the other day about the big guys getting going in crunch time and boy, it's September and they have gotten going."
Lee also hit a solo shot in the eighth inning of Saturday's 4-3 win.
Lance Berkman homered for the Astros, who lost two of three to the Cubs.
The Astros led 5-1 when Jason Kendall hit what looked to be a routine double play ball to shortstop Eric Bruntlett in the sixth inning. But Bruntlett dropped the bouncer, putting runners on first and second with no outs. Reliever Mark McLemore then walked pinch hitter Craig Monroe to load the bases, and Soriano followed with a sacrifice fly off Dave Borkowski.
Ryan Theriot followed with an RBI single to cut the Astros' lead to 5-3.
Borkowski limited the damage by getting Aramis Ramirez on a called strike to end the inning. Ramirez slammed his helmet and was immediately ejected by plate umpire Tony Randozzo after saying a few words to him.
"It was just a good feeling to finally come back," Lee said. "We just kept scratching and clawing, it seemed like we were never going to get there, but we were able to get some runners on base, score the runs and Dempster came in and did a good job of closing it down and we win the series. We didn't want to lose the series. That would've hurt a little bit."
Astros starter Woody Williams singled in the third, and Pence followed with a liner past shortstop Theriot that rolled all the way to the warning track for an RBI double.
Ty Wigginton drove a ball into left in the fifth inning that Soriano leaped for near the ivy. But he mistimed his jump and the ball bounced off the wall, allowing Berkman to score from first. With two outs, Bruntlett tested Soriano with another deep fly that fell for a double, scoring Wigginton and making it 5-1.
The Cubs got on the board in the third inning when Wigginton couldn't handle Lee's hard grounder at third. Theriot, who walked, stole second and took third on catcher Eric Munson's throwing error, scored on the play.
"I know they feel good about themselves over there but today was a tough one to swallow," Astros interim manager Cecil Cooper said. "We gifted them one in the third inning. It's the second day in a row that we've kind of given them a run and we need to tighten up our defense. I'm a little disappointed in that. I know it's not the best place to play defense, I know that. so we'll straighten that out."
Cubs manager Lou Piniella decided he will skip LHP Sean Marshall's next turn in the starting rotation. RHP Steve Trachsel, acquired in a trade from the Orioles on Friday, will take Marshall's spot. Trachsel will start on Tuesday against the Dodgers. ... Warnings were issued to both benches after Hill hit Berkman with a pitch in the fifth inning. Lee and Kendall were hit earlier in the game by Williams. ... Dempster has converted 13 straight save chances. ... Murton hit his second pinch-hit homer of the season.