Updated

Zach Johnson takes a one shot lead into the second round of the British Open at Muirfield Friday, heading a strong American challenge, with 11 out of the 20 players under par from across the Atlantic.

The 2007 Masters champions topped the putting figures on Thursday with just 26 taken, including a monster effort for eagle at the par-five fifth which set up the springboard for his round of five under 66.

Hard on his heels came veteran compatriots and former Open champions Mark O'Meara (67) and Tom Lehman (68), while tournament favourites Tiger Woods and Phil Mickelson were tied on 69.

Asked why American golfers were doing so well on what is the most traditional of British links courses, Johnson said it could be the uniqueness of the event.

"Maybe they have the same kind of mentality I have, where -- I'm having fun. I'm staying with a buddy and my caddie and our caddies, our physio guy, we're just having a good week," he said.

"I love it because we don't have it in the States. If we played this every week, it would be just another tournament."

If the Americans were thriving, the same could not be said for some of the big European names like Rory McIlroy who had a 79 and Luke Donald, who slumped to an 80 and who were both facing an uphill battle just to make the cut.

Former world number one McIlroy, mired in a season-long form slump brought on by an equipment change, described his state of mind out on the course on Thursday as being "unconscious" and "brain-dead".

He said he needed to throw off the shackles that were holding him back.

"I want to try to be here for the weekend. But the thing that I need to do tomorrow is just go out there and freewheel it and try and make birdies and try and play with that little bit of whatever it is I have usually," he said.

There were some unfamiliar names high up the leaderboard, with Spain's Rafael Cabrera-Bello tied for second with O'Meara and Indian qualifier Shiv Kapur on 68 along with Americans Lehman, Brandt Snedeker and Dustin Johnson as well as Spanish veteran Miguel Angel Jimenez.

Leading the home challenge on 70 was Martin Laird of Scotland and Oliver Fisher of England.

Defending champion Ernie Els was looking to improve on his opening round of 74, as was US Open champion Justin Rose on 75, while Australia's Masters champion Adam Scott was handily placed on even par.

With the sun once more shining brightly on the famed East Lothian course, which is holding The Open for the 16th time, conditions were once again expected to be fast and furious.

The pace of the sun-baked greens and tricky pin first round placings in particular brought a salvo of criticisms from some players, but some good early scoring Friday, following overnight hand-watering of the surfaces, indicated that the going might be easier this time around.

"The greens are expected to pick up pace during the day, but the dramatic increases of yesterday are not anticipated," the R&A said in a press release.