Johnson entered in a non-save situation and worked a 1-2-3 bottom of the eighth, getting Derek Jeter, Curtis Granderson and Alex Rodriguez to ground out.
"I feel back to normal," Johnson, who spent four days at a Baltimore hospital with food poisoning, said before the gaje. "My pants fit a little bit looser."
Johnson hadn't appeared in a game since April 22, when he picked up his seventh save of the season in the Orioles' 3-2 win over the Angels. The right-hander admitted on Monday afternoon that the first time he threw after being discharged from Saint Agnes Hospital, he didn't feel right, but Sunday's session was an improvement.
Showalter said before the game that he wouldn't try to ease Johnson back in with a no-pressure situation, adding that he'd try to use the righty as he has all year, in the closer's role.
Johnson -- who has converted his last 15 save opportunities, dating back to last season -- told Showalter he was available on Sunday, but he wasn't used as Baltimore rallied to score five runs in the ninth inning and defeat the Oakland A's, 5-2.
"He wasn't too happy with Buck yesterday," Showalter said with a grin. "[Johnson is] ready to go. He's eating normal food."