The ninth-year pitcher allowed six runs on eight hits over 4 2/3 innings for the Bisons, but the results took a backseat to his overall health.
"Yeah, he's good to go because he felt fine," manager John Gibbons said. "It's rare when you see guys, big league pitchers, go down and pitch in the Minor Leagues; they usually get pounded pretty good.
"I'd almost be surprised if he didn't, if you want to know the truth. Why that happens, I don't know, but you see it all the time. But the key is, he's healthy."
Johnson has been out for the past six weeks because of inflammation in his right triceps muscle. He made three rehab appearances -- one with Class-A Dunedin and two in Buffalo -- before getting cleared to start Tuesday in San Francisco.
The 29-year-old allowed a total of seven earned runs in his 11 2/3 innings at the Minor League level. He struck out 11 while walking four in his three appearances.