The 14-year-old hit it long but missed the fairway and his nerves were still frayed. He made a triple-bogey on the first hole, then a double-bogey on the second.
After five holes, he was eight-over and looking completely out of his depth. But Zhang managed to regain his composure and steadily grew in confidence.
He played his final 13 holes in one-over and signed for a nine-over-par 79, better than some seasoned professionals and just one shot more than Masters champion Bubba Watson needed in his opening round at the year's second Major.
"It was really tough. I didn't hit the ball quite well, but my putting was okay," said Zhang. "I'm actually okay with what I shot today. At least I broke 80."
Just making the 156-player field was a victory in itself for Zhang. He is the youngest player to compete in the event since World War Two and officials believe he is possibly the youngest ever, but the tournament's records are not fully comprehensive before 1945.
Zhang, an outstanding junior based in Florida, entered the US Open qualifiers as a longshot and did not make the field, although he came close and made the shortlist of alternates.
Three days before the tournament, he got the call that he was in after Britain's Paul Casey withdrew from the event because of a shoulder injury.
Suddenly, he was in the golfing spotlight and being compared to Tiger Woods and Rory McIlroy.
"I am really proud of myself, actually. Well I shouldn't say proud," he said. "I'm really honoured especially that those other guys that I watch on TV growing up and having them talk about me, that's really an honour."
Followed by a large gallery at the notoriously difficult Olympic Club course, Zhang showed some flashes of his amazing talent when he birdied the seventh and 18th, tricky holes which even Woods could only par.
"I kind of didn't care about how many over (par) I was even though it was like pretty high after the first five holes," he said. "I was just trying to forget about that, because I never had that big a crowd following me ever and never played a course like this before.
"I was really nervous the first few holes. But then they started cheering for me and I know I can kind of handle it a little bit so it got better."