According to A's manager Bob Geren, the move was made to allow Blevins some time to correct his problems on the mound.
The reliever struggled in Spring Training, posting an 8.31 ERA and surrendering 24 hits over 13 innings. Blevins' struggles continued into the season as he has allowed four runs on two hits over just two-thirds of an inning.
"I need him to go down there and get himself back to where he was last year, because he was very helpful to our team last year," Geren said of Blevins. "So it's a move that will strengthen our bullpen ... and give him the opportunity to get himself back to where he needs to be."
The 25-year-old was 1-3 with a 3.11 ERA in 36 games for the A's last year.
Giese, 31, who was claimed off waivers from the New York Yankees on April 8, has only appeared in one game for Sacramento this year, allowing just three hits and one run over four innings of relief. He is 1-5 with a 3.76 ERA across 52 2/3 innings in his Major League career.
David Singh is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.