Zach Johnson of the United States gestures on the 9th tee during the first round of the British Open Golf Championship at Muirfield, Scotland, Thursday July 18, 2013. (AP Photo/Scott Heppell)
AT A GLANCE
Event: 142nd British Open.
Length: 7,192 yards.
Field: 156 (149 pros, seven amateurs).
Prize money: 5.25 million pounds ($7.82 million).
Winner’s share: 954,000 pounds ($1.4 million).
Defending champion: Ernie Els.
TV: Friday: 3 a.m. to 2 p.m., ESPN; Saturday: 6 a.m. to 1:30 p.m., ESPN; Sunday: 5 a.m. to 12:30 p.m., ESPN.
Updated: July 19, 2013 8:57PM
GULLANE, Scotland — In rare sunny Scottish weather that Midwestern corn would love, Iowa native Zach Johnson fashioned a silky 66 on Thursday.
That 5-under-par performance put Johnson atop the leaderboard at the British Open at Muirfield. He holds a one-shot lead on two other unlikely contenders: Mark O’Meara, 56, who won the 1998 British Open, and Rafael Cabrera-Bello, a 29-year-old Spaniard who finished 81st last year in his only other British Open.
With some of the balmiest weather Scotland has seen in nearly 40 years expected to continue through the weekend, it’s anybody’s guess where the conditions are headed on a sun-baked golf course.
‘‘I’ll be the first one to tell you it was unfair,’’ O’Meara said. ‘‘But I’ve played in 25-plus Opens and I’ve seen conditions a lot worse than what they were out there today.’’
Many of the players are not happy, though. After shooting 69, Phil Mickelson urged the Royal and Ancient officials who oversee the tournament to use common sense.
‘‘Hopefully, they’ll let go of their ego and set it up reasonable, but you never know,’’ said Mickelson, who fears what might happen on Friday to the afternoon wave, which includes him and Johnson. ‘‘The greens are dying, and the holes are on edges of slopes that the ball just simply won’t stay.’’
Peter Dawson, chief executive of the Royal and Ancient, responded by saying, ‘‘We’re very conscious of player comment and we’re going to take that into account when we set up the course for [Friday]. We’re very satisfied that the course is playable, but very testing.’’
Johnson didn’t deny golfers are living on the edge at Muirfield.
‘‘The pins are getting very tricky and very difficult,’’ Johnson said. ‘‘What you’ve got to pay attention to, frankly, is color. If it’s green, it’s a little slower. If it’s brown, it’s going to continue to roll. But there are some dicey pins. I feel lucky to [have teed off] early in the day.’’
Johnson’s fast start helped him shake off the disappointment of coming up second in the John Deere Classic last Sunday to Jordan Speith, 19, who holed a dramatic bunker shot.
‘‘I’d forgotten about that until you mentioned it,’’ Johnson said. ‘‘No, I’m teasing. I think you have to [move on]. This game demands resilience. I don’t want to say I lost that golf tournament. What I’ve embraced is the fact that I’m playing great.’’
Speith shot 69 and is in the pack at 2-under with Mickelson and Tiger Woods, three shots behind Johnson.
While long hitters are eschewing the driver — Mickelson isn’t even carrying one — the straight-but-not-long Johnson hit driver six times, including a tee shot on the 559-yard fifth hole that helped set up an eagle. After a 5-iron to the green, Johnson drained a 45-foot putt to jump-start his round.
Going 5-under on his first seven holes, the 2007 Masters champion followed a 31 on the front nine with an even-par 35 on the second nine of Muirfield.
One linkster who’s not enjoying himself is Rory McIlroy, who got off to another hideous start, a 79, despite world-class skills.
‘‘You’ve just got to try and play your way out of it,’’ said McIlroy, who might be laboring under an intense burden of expectations. ‘‘It’s nothing to do with technique. It’s all mental out there. Sometimes I feel like I’m walking around out there and I’m unconscious. I just need to try to think more.’’
McIlroy got burned by the rock-hard greens more than once. But that, he knows, is not the heart of his troubles.