While Colin Montgomerie’s 71 left him borderline for qualifying for the final two rounds on one under, Clarke moved onto the 10 under par aggregate of 134.

Starting on the back nine he birdied the 11th, 12th and 15th to turn in 33.

Further birdies came on the first and second and after bogeying the next he recovered the dropped shot on the fourth and finished with two more birdies.

Clarke is seeking his first victory in America since the World Match Play title in San Diego two years ago - and his first anywhere since the European Open in Dublin last July.

After 36 holes the 33-year-old had yet to miss a fairway and had taken a mere 51 putts - 27 on the first day and 24 in his second round.

Also going well was England’s Luke Donald, five under for the day and six under overall with four holes to play.

The Beaconsfield golfer, a hero of the last two Walker Cups who came through the US Tour qualifying school, was in joint seventh place.

Montgomerie’s closing birdie could prove vital in staying in the £3million tournament, but he was struggling off the tee, hitting only 50% of fairways both days.