On Wednesday, the eve of the Northern Trust at Liberty National, Dan Fireman, the president of the club and son of its founder, Paul Fireman, was asked what he’d like the winning score to be this week. He joked about how his old-school dad would probably prefer it not to be very far under par. Well, with Wednesday’s heavy rain softening the course and virtually no wind during Thursday’s opening round, the Firemans did not get their wish. The players ate Liberty National for lunch Thursday, with the leaderboards bleeding with red numbers signifying many under-par scores. Eighty of the 120-player field posted rounds below par. Troy Merritt’s 9-under-par 62 led the way, with Dustin Johnson’s 63 right behind, followed by 63s by Jon Rahm and Kevin Kisner. Rory McIlroy, Tony Finau, Webb Simpson, and Justin Rose all posted 6-under-par 65s. “We were wondering how the course would hold up [Wednesday] night, and it was nice and soft out there,’’ Merritt said. “The greens were real receptiv...