South Korean Kim Si-woo had the best score at Pebble, a 66, while American Cody Gribble was best at Spyglass, also 66.
Day carded seven birdies in his 65, while two-time champion Dustin Johnson and 2017 victor Jordan Spieth also took advantage of the favourable scoring conditions on the Monterey Peninsula course as they opened with 66s, while last week's Phoenix Open runner-up Branden Grace returned an impressive five-under 67 at Pebble Beach. He won the event the previous three occasions, according to Golf Channel's Justin Ray.
Mickelson hit every fairway for the first time since 1998, hit all but one green in regulation and needed only 32 putts to get through the round. I asked myself, 'What's the right thing to do?' Hunter (Mahan) is my friend and I was here to caddie for him, so I called him.
"I don't think I've ever done that before, certainly in competition, so that was a big milestone for me".
The tournament, which sees professionals play alongside celebrities, is spread across three courses near the picturesque town of Carmel - Pebble Beach Golf Links, Spyglass Hill Golf Course and Monterey Peninsula. Fact is, "I had to really think about it. This was a day we had great weather, courses were very "scoreable", so you needed to take advantage of that".
MBS had threatened to use 'a bullet' on Jamal Khashoggi
She had also been promised access to forensic and police reports critical to her inquiry. "The Khashoggi murder is not an ordinary one".
Amazon's Bezos accuses tabloid of blackmail
The National Enquirer published a story last month that included lurid texts between Bezos and former TV anchor Lauren Sanchez . The new information reveals what has consumed the world's richest man since that publication revealed he was having an affair .
Measles cases confirmed in northwest Harris County
The health department said there are two other potential cases of measles that are pending as they wait for test results. For full protection, one dose is suggested at 12 to 15 months and another at 4 to 6 years old.
His round included a birdie on the par-three ninth, his 18th hole of the day, to leave him alongside Gay on seven under.
Hole of the day: After almost dumping his tee shot in the Pacific Ocean, Brandt Snedeker (who has won two of the last six of these tournaments) somehow made birdie from this preposterous position.
Johnson said last week's victory at the Saudi International on the European Tour was important.
Choi, who has won twice on the highly-regarded Japan Tour including the Casio World Open late a year ago, had never been to the United States before arriving in California this week. Both played at Monterey on Thursday. The U.S. Open returns in June, when Mickelson will get another shot to try to complete the career Grand Slam.
Hosung Choi, a two-time victor on the Japan Golf Tour whose extravagant body English after every shot made him an internet sensation, came back after a poor start.