"I'm not trying to give Michael any more or less information than what he needs," Matheny said. "And what he needs is you have today to go out, pitch and start a big league ballgame, which is pretty cool for a team that's right in the thick of things. We don't want to cloud it up for him at all."
The Cardinals are taking a cautious approach to the 22-year-old Wacha's work load. They had him on a six-day schedule at times with Triple-A Memphis.
"It's always walking that fine line of enough work and too much," Matheny said of Wacha, ranked by MLB.com as the Cardinals' No. 2 prospect. "You want to give him enough to where they're improving and going on a consistent basis to be ready for next year's challenges, but not too many for this year. There isn't a perfect number, but I think we've been pretty consistent with trying to give him as much time as we could in Triple-A and know that he's ready to go as long as we need him to go today."
As expected, the Cardinals optioned Carlos Martinez, who started Wednesday, back to Memphis to make room for Wacha on the active roster.
Chad Thornburg is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.