"I kind of know I belong," Wellemeyer said. "They gave me an opportunity and I'm going to make the best of it. I'm not trying to think too much out there, just pitching."
Rookie Joe Mather, recalled from Triple-A Memphis earlier in the day after struggling Chris Duncan was demoted, had a memorable debut both at the plate and in right field. He hit an RBI single in the seventh and made a diving catch in the second, fully extending to rob Adam LaRoche of a likely RBI double on a liner down the line, helping the Cardinals win for the sixth time in eight games.
Mather got a standing ovation after the catch on a ball Wellemeyer thought would go to the wall for sure. He was on his way to back up home plate.
"That'll go down as one of the best I've made, for sure," Mather said. "That's what you dream of."
Pujols' 14th homer was a two-run shot to straightaway center in the bottom of the first that answered Nate McLouth's 13th homer, a solo shot just over the right-field wall, in the top half for Pittsburgh. Wellemeyer added a sacrifice fly in the second and Cesar Izturis had an RBI single in the seventh through a drawn-in infield.
Pinch hitter Jason Michaels' three-run double off stand-in closer Ryan Franklin with two outs in the ninth, his second hit in 11 pinch appearances and first RBIs, cut the deficit to one before McLouth's comebacker gave Franklin his fifth save in seven chances.
"We had the right guy at the plate at the end," manager John Russell said. "We just couldn't finish it off."
Zach Duke (2-4) worked six innings and gave up three runs, two earned, and five hits. Duke's start was pushed back a day because a callus on his left middle finger. He allowed hits to three of the first six hitters before settling in.
"I'm glad I kept us in the game," Duke said. "At the same time, I didn't pitch well enough to win."
Wellemeyer (6-1) won his career-best fourth straight decision and doubled his victory total from last season, when the Cardinals picked him up on waivers from the Royals and gave him his first opportunity as a starter. He worked seven innings, a career high he's reached four times this season, and allowed one run and six hits.
"It woke me up a little bit in the first inning," Wellemeyer said. "Mather really helped me out and I ended up getting in a nice little groove."
Entering the season, Wellemeyer had a career record of 9-10 with a 4.98 ERA for four teams, making him the most likely pitcher to get bumped from the rotation when any of the team's several injured starters returned.
McLouth's homer was his first since May 17, and the Pirates' 32nd homer this month. Pittsburgh had only two runners in scoring position the last six innings against Wellemeyer.
Duke's throwing error led to an unearned run in the second. Second baseman Freddy Sanchez was late covering first base on a sacrifice bunt and Duke held up on a wild toss to first that dribbled into right field.
"I tried to throw the ball, it just slipped out of my hand," Duke said. "I hesitated and then I couldn't get a grip on it."
RHP Mike Parisi makes his first career start on Saturday for the Cardinals, subbing for injured Joel Pineiro. Parisi has a 2.87 ERA in 15 2/3 innings of relief over eight outings and was the opening day starter at Triple-A Memphis. ... Pujols also singled in the third and has 10 hits in his last 18 at-bats, raising his average to .364. ... La Russa will manage his 2,000th game with the Cardinals on Saturday. ... Pirates outfielders lead the majors with 34 homers. ... McLouth is 4-for-22 against the Cardinals, but with three homers and five RBIs. ... Wellemeyer had four strikeouts, giving him 36 in 37 2/3 innings for his career against the Pirates.