In his last start, after coming off the DL with a hamstring issue, Wainwright allowed three runs on six hits in a 5 1/3-inning no decision. This season, the righthander is 5-6 with a 4.50 earned-run average.
Wednesday marks the 300th career start for Wainwright, making him the fifth pitcher in Cardinals history to hit that milestone.
He will be opposed by 26-year-old righthander Daniel Mengden, who takes over the A's rotation for Frankie Montas, who's serving an 80-game suspension for use of PEDs. Menden is 1-1 with a 5.09 ERA this season.