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CHICAGO (AP) -- Randy Wolf's first shutout in more than four years gave the Houston Astros another lift in their impressive late-season surge.

Wolf pitched a six-hitter Wednesday night and the Astros ran their latest winning streak to eight games with a 4-0 victory over the slumping Chicago Cubs, who've lost a season-high five in a row.

"It's really gratifying the fact that I've been through a lot the last three or four years -- two surgeries -- and it's been a long way back," said Wolf, who's had procedures on both his elbow and shoulder since 2005.

"It makes it sweet to do it against such a good team and in Wrigley. It was exciting. I know it's been a long time. So it's nice."

Wolf (9-11) walked two and struck out eight, including Reed Johnson to end the fourth when they Cubs had two on. It was the 31-year-old left-hander's eighth career shutout and first since April 24, 2004, when he beat the Montreal Expos 7-0 while pitching for the Phillies.

Wolf needed 128 pitches to go the distance but was able to give the Astros' bullpen some rest.

"(Closer Jose) Valverde got on his knees before the game and did the sign of the cross four times begging for me to go nine," Wolf said.

Wolf got plenty of support Thursday night from Ty Wigginton, who continued his homer tear with his 22nd of the season and also made a great throw from left field to cut down the run. The win gave Houston its second eight-game winning streak in less than a month, matching an earlier one from Aug. 7-14. And now the Astros have suddenly re-emerged in the NL wild card picture.

"It gives us something to play for in September," Wolf said. "I know that we still have a ton of ground and some miracles for this to happen, but it's one of the reasons you don't give up."

The Cubs are stuck in their first five-game skid since dropping six in a row from May 27-June 2 last season. The NL Central leaders have 22 games left this season, 16 away from Wrigley Field.

"Basically they outplayed us," Cubs manager Lou Piniella said. "They outpitched us, outhit us. They just beat us. No excuses. ... You're going to have adversity along the way and we're having it right now. We'll see how we respond."

Despite the three game-sweep, the Cubs maintained their 4½ game lead over Milwaukee after the Brewers were beaten 9-2 by the Mets as New York completed a three-game sweep at Miller Park.

Wigginton, who homered 12 times in August, hit a two-run, two-out shot in the fifth off Ryan Dempster (15-6) to give the Astros a 3-0 lead.

The Cubs threatened in the bottom of the inning when Ronny Cedeno walked and went to second on a sacrifice.

When Alfonso Soriano singled sharply to left, Wigginton made a strong on-target throw to catcher Humberto Quintero, who reached back and nicked the back of a sliding Cedeno's jersey for the out. Astros center fielder Michael Bourn then made a nice catch of Ryan Theriot's long drive to center to end the inning.

"Soriano hit it hard and I got a great hop," Wigginton said. "That one ended up pretty easy just because the ball bounced up fairly high around my waist area. That made it easier to come through the ball and throw. Q did a great job of applying the tag."

The Astros made it 4-0 in the ninth when David Newhan and Bourn singled to put runners at the corners with two outs. Cubs' reliever Jeff Samardzija picked Bourn off first but when he was caught in a rundown, Newhan raced home. Cubs shortstop Theriot's throw to the plate was not handled by catcher Geovany Soto. Newhan was credited with a steal of home on the play and Theriot an error when Bourn made second.

Houston scored in the second with two outs on Hunter Pence's double, a walk and RBI single by Quintero.

Dempster went seven innings, giving up eight hits and the three runs. He vowed the Cubs would shake their slump.

"We're all right," Dempster said. "It's frustrating for everybody. You are going to go through bumps in the road and sometimes when they are late in the season ... they are magnified a little bit."

Game notes

Houston's victory was its 74th, surpassing last season's total when the Astros finished 73-89. ... Dempster laid down two more sacrifice bunts and leads the majors with 18. He is now 12-3 at Wrigley Field.