I hear ya, Malloy. That's what I thought too. But as I watched the match, Howard Cosell ( yes, he was commentating and he was orgasming over Nastase ) and John Newcombe mentioned this was his first match as a professional. It even said it on screen.
I think McEnroe had been in other tournaments before, most likely as an amateur. They mentioned his year at Stanford and that he was only 18. I'm just quoting what they said.