• Hero: Duncan snapped a 28-game home run drought with an upper-deck blast in the first inning.
• Unsung hero: Cards starter Braden Looper tossed seven scoreless innings.
• Rough debut: Phil Garner was fired on Monday after posting a 58-73 record, but the change to Cooper didn't reap immediate results.
• Quotable: "This wasn't what I planned." -- Cooper
-- ESPN.com news services
Cardinals 7, Astros 0
HOUSTON (AP) -- New manager. Same old floundering Houston Astros.
Phil Garner was fired on Monday and replaced by Cooper after Houston limped to a 58-73 record. But the Astros looked just as bad with Cooper in charge, plagued by mediocre pitching and feeble hitting.
"This wasn't what I planned," Cooper said. "We were all excited. This kind of takes the steam out of it."
Duncan, meanwhile, snapped a 28-game home run drought with a three-run drive into the upper deck in the first inning off Houston starter Woody Williams (8-13). Duncan was hitting just .167 with only three RBIs this month before Tuesday's outburst.
He's worked with hitting coach Hal McRae in recent days and worked out the glitches in his swing.
"I was just jumping at it too much," Duncan said. "Hal just asked me to stay back a little more, stay behind the ball. I started seeing the ball better, my pitch selection's gotten better. Maybe I can get something started."
Rick Ankiel and Aaron Miles added RBI doubles for the Cardinals, who've won six of their last eight and got back to .500 for the first time since they were 6-6 on April 16. Earlier this month, the defending World Series champions were eight games under .500 and eight games out of first place earlier this month.
"That's really the highlight of the day," La Russa said. "To finally get there, we ought to enjoy the moment. That's really special for this team."
St. Louis starter Braden Looper (11-10) pitched seven scoreless innings, allowing only four hits with four strikeouts. Looper has won five of his last nine starts.
The Cardinals stayed two games behind Chicago in the NL Central. The Cubs beat second-place Milwaukee 5-3 on Tuesday night.
"We're not done yet," Looper said. "It would've been easy to make excuses, but the guys in this room have continued to battle."
Williams allowed six runs on eight hits as the Astros lost for the sixth time in eight home games.
Cooper, Houston's bench coach for the past three seasons, addressed his team before batting practice on Tuesday, preaching about eliminating mistakes and playing with more enthusiasm. But second baseman Craig Biggio mishandled Ankiel's grounder as he tried to backhand it with one out in the first inning, a sign of the night to come. It was ruled an infield hit.
After Jim Edmonds singled with two outs, Duncan hammered a 3-2 changeup high into the right-field seats, his first homer in 68 at-bats.
Biggio beat out an infield hit and Hunter Pence walked leading off the Astros' first. Looper then struck out Lance Berkman and Carlos Lee and Ty Wigginton lined out, a blown scoring chance typical of Houston's season.
"That first inning was everything," La Russa said.
Yadier Molina led off the second with a single and went to second on Looper's sacrifice bunt. Miles then doubled down the right-field line to make it 4-0.
Looper breezed through the first three innings, retiring the nine batters he faced after Pence walked. Berkman led off the fourth with a single to left and out later, Wigginton got hit by a pitch. Luke Scott then grounded into an inning-ending double play, killing another potential rally.
Looper has allowed four hits in each of his last four starts.
"It's been a process all along," he said. "I've taken my bumps and bruises and had my bad outings. I've had it handed to me and I've learned from that."
Ankiel and Albert Pujols hit consecutive one-out singles in the fourth, and Edmonds walked to load the bases. Cooper then made his pitching change, calling on left-hander Mark McLemore to relieve Williams.
It backfired -- Duncan and Scott Rolen lined back-to-back RBI singles to put the Cardinals up 6-0.
Houston right-hander Travis Driskill, called up from the minors last week, relieved McLemore to start the sixth and Miles led off with his second double. He went to third on David Eckstein's ground out and scored on Ankiel's double down the right-field line.
The Astros were shut out for the sixth time this season.
Cooper planned to tinker with his lineup before Wednesday's game.
"Today, I just tried to get as much feedback as I could and everyone agreed that I should just stay with the same lineup we had," he said. "Tomorrow, there will probably be a couple of changes."
La Russa won his 1,041st game with St. Louis, tying Red Schoendienst as the franchise's winningest manager. ... Former Astro Russ Springer pitched a perfect eighth in relief of Looper. ... Looper didn't allow a run for the first time since May 12. ... Biggio got his 3,041st career hit.