Phil Mickelson is one shot off the lead after a 67 at Doral

Two 37-year-old relative unknowns were at the top of the leaderboard on the first day of the WGC-Cadillac Championship, while several of the world’s top golfers struggled Thursday on the Blue Monster.

Australian Marcus Fraser, who is ranked 58th in the world, and American Scott Piercy, ranked 48th,...