Wellemeyer eliminated the over-the-head move, and simplified his delivery between starts, and the result led to a 2-1 win on Monday over the Arizona Diamondbacks before 25,014 at Chase Field.
"I felt a lot better out there, keeping my shoulders square to the plate and not wrapping," Wellemeyer said. "It helped me out immensely."
Wellemeyer was supported by two home runs, as Albert Pujols hit his fourth of the young season in the fourth inning off D-backs southpaw Doug Davis, and leadoff hitter Brian Barden hit an opposite-field blast in the eighth to break a 1-1 tie off Davis, who fell to 0-2.
"I was seeing the ball well tonight," Barden said. "He got one out over the plate, and I got enough of it to drive that way. I was looking [away] over the plate all game. It was a cutter, and I was able to hit one at the right time."
Barden's home run was the first of his career, coming against the team that drafted him in 2002 and with which he made his big league debut in 2007.
"It's a great feeling," Barden said, "and I have no hard feelings against them."
Barden's home run made Wellemeyer a winner after he was lifted for a pinch-hitter one batter earlier.
Wellemeyer went seven innings, allowed seven hits, one earned run, struck out four and didn't walk a batter.
"He was feeling good, and he was sharp," Cardinals manager Tony La Russa said. "He has a good assortment and he used it today. He and [catcher Jason] LaRue really matched up well.
"He hit his spots most of the night, and when he does that, he's got plenty of stuff to win."
The only run he gave up came in the fourth when D-backs first baseman Chad Tracy doubled home Conor Jackson.
The D-backs' other main threat came in the third, when Felipe Lopez doubled with one out to put runners on second and third. Nothing came of it, however, as Wellemeyer induced a pop to second base by Chris Young and grounder back to the mound by Stephen Drew to close out the inning.
"That's a good lineup, and I wasn't really all that excited about facing them," Wellemeyer said. "Halfway through the game, I felt more comfortable with my delivery after going all year going over my head."
After Barden's heroics -- La Russa called it Hollywood-ish -- it was up to the bullpen to secure the win.
Kyle McClellan got the first two outs in the eight before giving up a single to Young, who advanced to second when Chris Duncan bobbled the ball in left field, and Dennys Reyes relieved with the tying run at second and got Drew to ground out to Pujols.
Ryan Franklin gave up a harmless infield single to Mark Reynolds in the ninth before earning his first save of the season.