Bailey, nursing a strained rib cage muscle back to health, played catch from a distance of 120 feet before throwing all of his pitches in a bullpen he deemed he "dominated."
"No hits allowed," Bailey said with a smile.
That's good news for the A's, who hope to have their closer back on the upcoming seven-game homestand against Toronto and Tampa Bay that begins Monday. If Bailey experiences no ill effects from Sunday's session, he said he'd likely throw one more bullpen before potentially pitching in a simulated game and being activated thereafter.
"He needs a couple more times off the mound," Geren said. "But, today, obviously was a big step. Him throwing off the mound at that kind of effort level, that's a real positive step.
"We're optimistic based on how he feels right now."
Bailey hasn't pitched since July 20, a time when he had not allowed a run in 13 of his past 15 appearances.