Colin Montgomerie celebrated his 43rd birthday by taking the early lead in the Johnnie Walker Championship second round.

A second five-under-par 68 for a total of 10-under-par 136 gave the Scot a three-stroke advantage over Sweden's Robert Karlsson (68) and Denmark's Soren Hansen (70).

Despite hauling himself to the top of the leaderboard, Montgomerie's round was spoiled by another mishap on a finishing hole.

On Sunday Montgomerie lost the U.S. Open by double-bogeying the 18th at Winged Foot. In the first round at Gleneagles he bogeyed the 18th to miss out on a share of second place overnight and this morning he missed a three-foot putt at the last to deny himself a larger leading margin.

After reaching his final green in two at the par-five finish, Montgomerie three-putted from 20 feet.

"I just don't know what's going on here," said a perplexed Montgomerie after signing for a round that contained six birdies and one bogey. "That's my third round in a row and that's not good at all. If I can't two-putt from 20 feet there's something wrong. There was nothing difficult about it at all.

"I've got to get it right for 18 holes. It tarnished the US Open, it tarnished yesterday and it's tarnished today."

His final blemish excepted, Montgomerie was happy to be leading after surviving only 12 holes last year before retiring with bruised fingers.

First round leader Thomas Bjorn is among the later starters.

Stephen Browne leads the Irish challenge on four-under with Paul McGinley, David Higgins and Peter Lawrie a shot further back having completed their second rounds.

Damien McGrane avoided missing the cut after he rallied on the front nine having started on the 10th. On three over par with just three holes to play, McGrane needed a strong finish. He delivered with consecutiove birdies on each hole to just finish on the right side of the cut, on level par.

Michael Hoey will not be around for the weekend after finishing on six-over.