It was one of their best moves of the summer.
Chris Duncan, the incumbent left fielder and No. 2 batter for most of July, enjoyed a remarkable August, winning the National League Rookie of the Month Award sponsored by Bank of America.
The 6-foot-5 left-handed swinger crushed National League pitching, batting .361 (30-for-83) with nine homers, 14 RBIs and 20 runs scored over 25 games.
"Duncan is swinging the bat really well," teammate Preston Wilson said.
The son of Redbirds pitching coach Dave Duncan, Chris helped the Cardinals extend their lead over the Reds in the NL Central. On Aug. 1, the Redbirds led by 3 1/2 games. Entering Wednesday's action, Duncan's offense had helped the team extend the advantage to six games.
Batting in front of reigning NL MVP Albert Pujols, Duncan saw a steady diet of strikes. He often took advantage early in counts, belting several key homers off first pitches, including a pinch-hit homer on the initial offering he saw from Sergio Mitre against the Marlins on Aug. 31.
The shot tied the game at 2 and started a four-run rally that provided the Redbirds with another victory.
"I wanted to be really aggressive and I wanted to hit the first fastball that was in the strike zone," Duncan said of the homer. "He tried to get ahead with a fastball, and he left it over the plate."
That same approach paid dividends several times -- especially in critical series. Duncan saved his highest outputs for the two sets against the hard-charging Reds. The left-hander scorched Cincy pitching, registering an astronomical .593 average (16-for-27) with four homers.
One of his best games of the month came Aug. 10 against the Reds. Duncan belted two homers against Cincinnati, including a fifth-inning blast that kick-started a three-run rally and put the game out of reach.
His batting eye also improved. Rather than chasing off-speed pitches off the plate, Duncan improved his strike-zone judgment. He drew 12 walks in August -- nearly twice as many as his previous monthly best -- and registered a .438 on-base percentage.
"He has a better-than-average eye for a young hitter," Cardinals manager Tony La Russa said.
The eye also helped the 25-year-old collect a nine-game hitting streak from Aug. 12-22. During the span, Duncan batted .531 with four homers.
Duncan has also vaulted into Rookie of the Year consideration. Among rookies with at least 200 at-bats, the Cardinals' left fielder is second in average (.320), first in on-base percentage (.383) and first in slugging by nearly 90 points (.606).
His August was also better than several NL rookies nominated for the award, including the Dodgers' Chad Billingsley (3-0, 1.50 ERA), the Phillies' Cole Hamels (4-2, 2.43 ERA), and one of the Rookie of the Year front-runners, Marlins shortstop Hanley Ramirez (.327 average).
Conor Nicholl is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.