St. Louis' Carlos Martinez and San Diego's Colin Rea were in line to start Tuesday, and both were bumped back to Wednesday afternoon. Jaime Garcia gets the ball Wednesday night for the Cardinals, as expected.
San Diego, on the other hand, decided to shuffle its rotation a bit for the nightcap. Long reliever Paul Clemens will make his first start for the Padres, after they claimed him off waivers at the end of June. He's pitched 3 1/3 scoreless innings in relief for San Diego.
That decision pushes Andrew Cashner to Thursday, keeping the Padres' rotation fresh through the rest of their road trip -- which now consists of nine games in eight days.
The Cardinals, meanwhile, do not have an off-day until Aug. 1, meaning they'll have to fill a vacant spot in their rotation by the weekend -- or opt to pitch someone on short rest.
In their first twin bill of the season, the Padres swept the Cubs in Chicago on May 11 after a May 9 rainout at Wrigley Field -- their only other postponement this year.
The Cardinals were swept in two of three doubleheaders last season, losing to the Cubs on July 7 and the Braves on Oct. 4.
The last time Busch Stadium played host to a pair of games in the same day, the Cubs and Cardinals split on Aug. 30, 2014.
The Padres and Cardinals last contested a doubleheader on Sept. 29, 1999, which St. Louis swept. San Diego hasn't lost a twin-bill sweep since.
AJ Cassavell covers the Padres for MLB.com. Follow him on Twitter @ajcassavell. This story was not subject to the approval of Major League Baseball or its clubs.