Clarke birdied the first three holes at the Taiheiyo Club Gotemba Course and added four more birdies before dropping his first shot on the penultimate hole.
Starting from the tenth hole, Clarke holed a 15 foot birdie putt. He hit his second shot into a bunker on the following par five hole but his approach shot left him a ten foot birdie chance, which he duly took, before he went on to hole a five foot putt for a third straight birdie.
His only bogey came on the eighth hole when he missed the green with a nine iron from the fairway and failed to get up and down.
"I started pretty well today, but ended poorly the last couple of holes. I don't know why, probably because of jet lag," said Clarke.
Ryder Cup team-mate Lee Westwood, a three-time champion from 1996 to 1998, was tied for seventh place on 68 with eight Japanese, including local top money earner Shingo Katayama.
Graeme McDowell of Northern Ireland was tied at 16th place following an opening 69.
Courtsey of: www.europeantour.com