Mengden will take the rotation spot of Frankie Montas, who was suspended 80 games on Friday for violating Major League Baseball's performance enhancing drug policy.
This will be Mengden’s second stint with the A’s this year. The 26-year-old went 1-1 with a 5.09 ERA in five games before being optioned back to Las Vegas on June 6.
“He just needs to keep his pitch count in control,” A’s manager Bob Melvin said. “He’s got the stuff to be able to pitch behind [in the count], but you don’t want to do that. You’re not going to have consistent success with that.”
Mengden has never faced the Cardinals, but he has had success in Interleague Play, winning his last three starts against National League foes dating back to Sept. 15, 2017. He has two two-hit shutouts during that span.
“His stuff is good,” Melvin said. “I think when we saw him in the past, he’s thrown a lot of pitches, and even when he’s pitching OK we had to get him out a little bit early. So it is about getting ahead of the count, getting strike one and keeping his pitch count under control.”
Injury updates: Manaea, Herrmann
• There is no timetable on how long Sean Manaea will be shut down. Melvin said the soreness the lefty felt on his right side is symptomatic, so the setback is based on how he feels. Manaea has been on the 60-day injured list since February as he works his way back from left shoulder surgery. He threw 60 pitches in a simulated game at the A’s Minor League complex in Arizona on Thursday.
• Melvin said Chris Herrmann will have to catch back-to-back nine-inning games before the team considers activating him from the injured list. Herrmann, who is working his way back from right knee surgery, is on a rehab assignment at Las Vegas.