Right-hander P.J. Walters will make his Major League debut on Friday afternoon, with Lohse pushed from Friday to Saturday and Wellemeyer from Saturday to Sunday. Carpenter's spot would have come up on Sunday, but this configuration makes more sense for a variety of reasons. Carpenter was placed on the disabled list on Wednesday due to a left rib cage injury. It's uncertain how long he will be out.
For Walters, a Friday start would put him on five days' rest, as opposed to seven if he'd pitched on Sunday. Additionally, the Sunday game is a nationally televised ESPN game, while Friday's assignment might put a little less pressure on Walters.
"The fact that Friday is his perfect day counts for a lot," said manager Tony La Russa.
The greatest benefit, though, is likely for Lohse. He worked hard to go seven innings in his season debut, then endured a difficult ninth inning to pitch a complete game on Sunday in St. Louis. Having an extra day of rest should benefit the righty, and it can't hurt for Wellemeyer either.
"You had a choice to make," La Russa said. "If Carp was ready, there would be no choice. But once you have a spot open, and it happens to be Walters' day, Lohse has had two [difficult] games as far as work, so it's nice to have the extra day. It worked out nice."
It's unclear what the corresponding roster move will be when the Cardinals bring Walters up for Friday's game. They could send a pitcher down, but La Russa also said it's possible that the club will go to 13 pitchers for a brief period. Both Tuesday and Wednesday's games in Arizona taxed the St. Louis bullpen.
That decision might hinge partly on how long the club envisions Walters being on the big league roster. One option would be to call him up at the expense of a position player, then send him back down immediately after the game -- keeping eight relievers and four starting pitchers for a period of time. The Cardinals could set up their rotation so that they wouldn't need a fifth starter again until Saturday, April 25 at home against the Cubs.
La Russa declined to discuss whether Walters would be up for one start or an extended period of time.
"The only way you can answer that question is if you have a crystal ball," he said. "I think we're just trying to deal with what we have at the time. Obviously the better he does, the more chances he gets."
Matthew Leach is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.