Golf's new "Big Three" led by Jason Day and perennial US Open nearly man Phil Mickelson were set to be tested Thursday as the second major golf championship of the season teed off at formidable Oakmont. A chance of thunderstorms later meant a possibly messy ending to the opening day of action, but morning starters including defending champion and world number two Jordan Spieth, world number three Rory McIlroy and British Open champion Zach Johnson, could expect to enjoy the rain-softened course before more threatening weather arrived. "You have to be so disciplined," McIlroy, the 2011 US Open winner, said.
