He had fought as hard as he could to get his way around the notoriously difficult Olympic Club layout, but the course ate him up and he signed for an eight-over-par 78.
"It beat me up today," he said. "It's beating me by eight right now.
"This course is just not good for me. It's a lot better than I am."
Watson, a self-taught maverick who has risen to the top through improvisation and a bag full of tricks, predicted before his opening round that he would struggle.
The big-hitting left-hander feared his game was not suited to the course because of its narrow fairways and long rough. He was no closer to working out how to play it after his first round.
"That golf course is too tough for me," he said.
Two months ago, Watson won the Masters in brilliant fashion, pulling off a miraculous approach shot from the rough to beat South Africa's Louis Oosthuizen in a play-off.
But the 33-year-old has not been at his best since then, juggling his golf game with new demands on his time, which have included everything from appearances on TV talk shows, being presented with the keys to the city of his hometown and changing diapers as a first time father.
He has played just two events since the Masters, finishing tied for 18th at the Zurich Classic in New Orleans, a tournament he won in 2011, then missing the cut at the Memorial two weeks ago.
His round included a bit of everything, a birdie, seven bogeys and a double-bogey on the par-4 18th hole, leaving him needing a good round on Friday to make the cut.
"I just couldn't get anything going. I never got any rhythm, everything was just a little off," he said.
"It's disappointing starting off like this, it doesn't matter what tournament.
"I've got to just come out and try to play it (the course). Obviously it beat me today."