Spencer Levin and Kyle Stanley both shot rounds of 62 to finish the first day with a share of the lead at the Farmers Insurance Open at Torrey Pines.
The pair are one shot ahead of Bill Haas with Rod Pampling, Vijay Singh, Josh Teater and John Huh in a four-way tie a further shot back.
Levin shot a 29 on the back nine of the North Course after seven birdies with ten overall for a career-low.
He said: “My mind was pretty clear, and it just worked out good. I played really well on that back nine.
"I had good looks and was putting well so it kind of added up.”
Stanley’s 62 was also a career-low and it included an eagle on the 18th hole.
He said: "The course is in good shape, the fairways are nice, the greens are soft, but you can just be pretty aggressive with your irons.”
The top 12 players on the leaderboard all played the North Course, which is generally regarded as the easier of the two.
The field will switch courses on Friday and everyone who survives the cut will play the final two rounds on the South.
Three-time champion Phil Mickelson, shot a 77 on the South, the second-highest score ever on the course that hosted the 2008 US Open and left him in a tie for 147th.
Sweden’s Jonas Blixt was the leading European on two under, one ahead of a group including Justin Rose and Ernie Els.
