In his first pinch-hitting assignment of the regular season, Duncan cracked a long solo homer that gave the Cardinals a 3-2 win and a sweep over the Pirates.
"I was a little upset I didn't swing at the first couple of strikes," Duncan said.
La Russa said, "I wasn't thinking home run, but I thought he would get on base ahead of Albert (Pujols)."
The Cardinals scored just nine runs in three games -- three in each -- but that was enough to sweep the series, raising St. Louis' record at PNC Park to 37-15.
Closer Jason Isringhausen, who worked back-to-back assignments on Monday and Tuesday for the first time since he had left hip surgery last September, was deemed unavailable Wednesday, so setup man Ryan Franklin got the call. Franklin got the final out of the eighth with two runners on base and then worked a scoreless ninth for his first Cardinals win.
The Cardinals moved into first place in the National League Central on the strength of a four-game winning streak. But, in seven of their nine games, they have scored three or fewer runs.
CARDINALS 3, PIRATES 2: The Cardinals scored three runs for the third consecutive game in the series and won all three. They erased a 1-0 deficit in the fifth when David Eckstein singled home a run and Preston Wilson legged out an infield single with the bases loaded. The bullpen of Russ Springer, Randy Flores and Ryan Franklin was scoreless over the last 2 1/3 innings.
NOTES AND QUOTES
--1B Albert Pujols is off to the worst start of his career, hitting .176. He is 0-for-10 against left-handed pitching and 0-for-9 with runners in scoring position.
--RHP Adam Wainwright was allowed to throw 113 pitches as the Cardinals tried unsuccessfully to get him through seven innings Wednesday. He allowed two runs in 6 2/3 innings.
--SS David Eckstein, who went 2-for-5 Wednesday, is 6-for-12 against left-handed pitching.
--Cardinals manager Tony La Russa is keeping his team's hot streak in perspective. "Losing three in a row didn't mean we were a bad ballclub. And winning five out of six doesn't mean we're a juggernaut either. We've got a lot of work to do," he said.
--2B Aaron Miles earned a second consecutive start Wednesday after getting four hits on Tuesday. He was hitless in three at-bats Wednesday but walked and scored the first run.