"We felt like we hopefully gave it enough time to go away, and it didn't, so we gotta give him some rest," said A's manager Bob Melvin.
Overall, O'Flaherty was 0-2 with an 11.57 ERA in eight outings -- a disappointing start to what was expected to be a big year for the veteran, who hasn't enjoyed a full season since 2012. He underwent Tommy John surgery in the middle of the 2013 season with the Braves and returned to make 21 appearances for the A's last year, pitching to a 2.25 ERA.
Alvarez rejoins the A's just 10 days after being optioned to Nashville. He made just one relief appearance for the Sounds, back on Tuesday, and hopes to showcase better command in his second stint with Oakland, after allowing nine runs -- seven on April 21 -- in six relief appearances for a 12.00 ERA.
"I know I gotta get out there and throw a few more strikes," said Alvarez. "I don't think it's anything mechanical, I just gotta go out there and do it. Seems like every time I walk guys, it's just one pitch I gotta make better."
Jane Lee is a reporter for MLB.com. Read her blog, Major Lee-ague, and follow her on Twitter @JaneMLB. This story was not subject to the approval of Major League Baseball or its clubs.