"I know he felt good about it, and we thought we saw better velocity in the simulated game and the bullpens proceeding that," A's manager Bob Melvin said.
Doolittle allowed a solo home run in Tuesday's 21-pitch outing, but also struck out the side. He'll pitch again Friday with Nashville and is expected to be activated from the DL during the A's homestand next week.
"From what I understand," Melvin said, "it's the best he's felt and the most comfortable he's felt on the mound yet."
Jane Lee is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.