The Portrush rookie, who is attached to the tournament's host club Kungsangen, compiled a neat card of seven birdies to lead Australian Adam Scott by one shot.

Two shots further back on five under were English trio Warren Bennett, Matthew Cort and Grant Homerton.

McDowell, a member of Peter McEvoy's victorious 2001 Walker Cup team, started on the 10th and despite a slow start kept bogies off his card throughout the round.

"I didn't feel that good for the first five or six holes," said McDowell, who is playing only his fourth European Tour event.

"But I scrambled and hung in there and things got better from then on.

"I'm very happy to be here and break the course record is a dream start."

McDowell, a former University of Alabama student was the top-ranked collegiate golfer in the United States last term.

He had a stroke average for the 2001-02 season of 69.6 - better than Tiger Woods when he was a student at Stanford.

Scott, meanwhile, outscored playing partner and defending champion Colin Montgomerie by five shots to equal the old course record.

The Australian was making the most of a lesson from coach Butch Harmon at Muirfield after a poor Open crowned a string of missed cuts.

"I'm very happy with that start, it's nice to put a low number on the board, it's been a while," said the 22-year-old, who has Montgomerie's former long-term caddie Alastair McLean on the bag.

"Some bad habits in my technique were killing me and I was not able to sort them out before the tournament came round.

"I was trying to come up with a quick fix and it was not working so well."

Montgomerie, starting at the 10th, made a poor start after an hour's delay for heavy rain and dropped two shots in his first four holes.

But despite two further bogies he picked up five strokes, including two birdies in his last two holes.

"I didn't really perform all that well and missed a lot of shots on the wrong sides of the greens," said the 39-year-old Scot.

"But I managed to shoot under par and I'm not in a bad position to try and go out and shoot low tomorrow in the second round."

First-round leaderboard (GB&Ire unless stated):

-7 Graeme McDowell
-6 Adam Scott (Aus)
-5 Warren Bennett, Matthew Cort, Grant Homerton
-4 Niclas Fasth (Swe), David Lynn, Michael Campell (Nzl), Jesper Parnevik (Swe), Ignacio Garrido (Spa), Ronan Rafferty, Marcel Siem (Ger)