Doolittle, who saved the last two games against the Angels, is 1-3 with 20 saves and a 2.28 ERA in 54 relief appearances. He has walked five and struck out 80 in 55 1-3 innings.
Doolittle leads American League relievers in opponents' on-base percentage (.190), ranks fifth in strikeouts, sixth in opponents' slugging percentage (.256) and eighth in saves and opponents batting average (.171).
Right-hander Dan Otero was recalled from Triple-A Sacramento. Otero was on the A's Opening Day roster and was 7-1 with a save and a 2.28 ERA in 56 relief appearances when he was optioned to Sacramento on Thursday.