After the game, O'Day shook as he spoke by his locker.
"You have to go out there and do your job, but you can't -- it's something you don't just block out, especially a couple of hours after you find out," O'Day told reporters in Cincinnati. "I've never really dealt with anything like that before. It certainly was on my mind."
The two came up together in the Angels system, parting ways prior to this season. O'Day went to the Mets, with whom he is looking to carve his niche as a sidearming specialist out of the bullpen. Adenhart, one of the game's top pitching prospects, remained with the Angels, where he made a sparkling season debut on Wednesday night, picking up a no-decision in Los Angeles' loss to Oakland.
Within hours, Adenhart was pronounced dead at the UC-Irvine Medical Center.
"Last year, he had all the talent in the world but couldn't figure it out," O'Day said. "Then he figures it out, and six hours later he's gone."
O'Day learned of his friend's death just hours before the afternoon game in Cincinnati. There was precious little time to let the news sink in, let alone to grieve. And though he told Mets manager Jerry Manuel that he was fine to pitch, O'Day was understandably shaken.
"I asked if he was OK, but you don't really know," Manuel said. "I don't know him well. Some guys like to or want to perform to kind of dedicate that to what they just went through, and you don't know."
O'Day said that he had been meaning to give Adenhart a phone call, and he regretted not sending his former teammate a text message to congratulate him on Wednesday's start.
"I sent him one today," O'Day said after Thursday afternoon's game. "But that doesn't really do much good."
Anthony DiComo is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.