The popular American and current world number 12 decided it would be in his best interests to rest up fully before this year’s U.S. Open, taking place at San Francisco’s Olympic Club from June 14-17.
“I think, mentally, I’m a little bit fatigued,” said the four-time major champion after his round.
“The course here is in such great shape but I’m hitting it so poorly. I have to look at what’s best for me to play in the U.S. Open and I’m going to take the next few days to kind of rest up.
“Certainly, I’m disappointed with how I played today, but I’ve got to be more big-picture orientated and think about the U.S. Open and what’s best to get my best golf out there. I need the next few days to rest.”
Mickelson said his fatigue was a result of last week’s trip to Europe, where he took wife Amy to celebrate her 40th birthday after three straight weeks of golf on the PGA Tour.
The 41-year-old admitted it was the first time he had quit a tournament without suffering an injury.
“I feel like it’s the responsibility of a player to see through your commitment to play and finish the tournament,” he said.