Osuna was placed on administrative leave May 8 after he was arrested by Toronto police on suspicion of assaulting a woman. McCullers has a 3.93 ERA through 126 innings this season.
Osuna took the mound for the first time since serving a 75-game suspension under the league's domestic violence policy, a penalty outranked by just two previous bans in severity.
The Houston Astros continue to be criticized for their acquisition of closer Roberto Osuna from the Toronto Blue Jays, and continue to try to mend fences with their fans and the community in light of it.
The former All-Star was inserted into the game in the bottom of the eighth inning in San Francisco, though the Astros' official Twitter account made no mention of their controversial acquisition's debut at that juncture.More news: Ruby Rose Is The CW's Batwoman
Osuna offered few details about the meeting Sunday morning in the Astros' clubhouse at Dodger Stadium and did not discuss the case pending against him.
"On August 4th, Roberto Osuna willfully and successfully completed his Major League Baseball domestic violence program requirements", the statement began.
"We are now focused on ensuring that Roberto makes a positive impact off the field while he is a member of the Houston Astros". We welcome being held accountable for all of our personnel decisions. We are strong believers in protecting the rights of victims and remain committed to having a positive impact on our community. He posted 39 saves and a 0.86 WHIP a year ago.