One hour later, play was abandoned for the day with unheralded Americans Rick Lamb and Joel Dahmen, and South Korean Noh Seung-yul, sharing top spot on the leaderboard after opening with four-under 68s.
All three had started out on the Spyglass Hill layout, one of three venues being used for this week's PGA Tour event.
Seventy-four players in a field of 156 had completed their rounds and organisers hope to get the tournament back on track on Friday, though weather forecasts predict a 50 percent of rain at Pebble Beach on Friday morning.
"We only played four holes in the rain," Day told Golf Channel after mixing four birdies with two bogeys at Monterey Peninsula Country Club. "It's hit and miss ... sometimes you can get lucky with the draw, especially where you are playing.
"If you were playing at Spy today, it definitely helped a little bit, especially with some of the cover in the trees, but you've just got to take what you can get and try and win the tournament at the end of the week."
Given the weather conditions, Day was thrilled with his opening round.
"I feel pretty good with how things are going, coming out today and shooting a couple under par," said the 29-year-old, a 10-times winner on the PGA Tour.
"The hardest part about today was actually committing to the shot more so than anything because you had a lot of side winds. I'm looking forward to Spyglass tomorrow."
Among the other high-profile names competing this week, world number six Jordan Spieth was three under after 16 holes at Monterey Peninsula while four-times champion Phil Mickelson was one under after 17 on the same layout.
(Reporting by Mark Lamport-Stokes in St. Augustine, Florida; Editing by Frank Pingue)
