Lomas, 26, playing in his first British Open, had to overcome his own quivering nerves to get around the windswept Turnberry links without a bogey.
"It was a struggle at the end. I was getting very nervous," said Lomas, a career struggler who has yet to win.
With more than half the 150-man field still on the course in deteriorating weather, Lomas held a one-shot lead over Andrew Magee, who led a surprisingly strong American presence.
Magee, a casual, easy-going man who used a 17th hole eagle as the springboard to a 67, refused to be caught up in any nationalistic partisanship, however.
"I'm not representing the U. S. This isn't a Ryder Cup. I'm just representing myself, trying to have a good time and play as well as I can," he said.
Until this morning, no Americans were listed among the top 10 favorites by Britain's legal bookies, and no American had odds of better than 33-1.
That changed overnight, however, when about one-half million British pounds were wagered on five-time Open champion Tom Watson, reducing the odds to 16-1 just before his early morning tee time.
Watson responded with a 2-under-par 68 that put him two off the early lead and in a tie for third with fellow Americans David Edwards and Loren Roberts, Australian Peter Senior and Jean Van de Velde of France.
Nick Price of Zimbabwe, a three-time winner on the American tour this year, was in a large group at 69.
Watson, in the third group off the tee, played in partly sunny weather with light winds for most of his round and got his score on the board just as the weather began to change.
A freshening wind picked up and clouds began to roll in as he played the final few holes. By early afternoon, a light rain had begun to fall.
Roberts, 39, who scored his first career victory earlier this season in the Nestle Classic in Orlando, Florida, once had it 4-under par, but bogeyed two of his last three holes.
"I think the leaders, at the end of the day, will shoot very good scores on the front nine, maybe 4 or 5 under," he said. "But it's going to be very difficult to stay even par on the back."
South African David Frost served as another early example. He was among the leaders most of his round, then bogeyed three of his last four holes and finished at par 70.
Watson, who has won only once in the United States in the last 10 years, said he was "happy with the score, but I did it the wrong way. I played the front, the downwind holes, in par, then got my score coming in, playing into the wind."
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