Graeme McDowell is ten strokes behind a red-hot Justin Thomas after opening with a frustrating 73 in the inaugural CJ Cup @ Nine Bridges in South Korea.

Playing on a sponsor's invitation, the Portrush native made an eagle, two birdies and five bogeys in a one-over-par round at the Jeju Island venue as Player of the Year Thomas fired an nine-under 63.

Thomas won five times last season, including his first major at the US PGA before capturing the FedEx Cup.

He made two eagles, seven birdies and two bogeys in his eight-under-par round to lead by three strokes from Chez Reavie, Malaysia's Gavin Green, Scott Brown, Marc Leishman and Patrick Reed.

McDowell, 38, started on the back nine and went out in one-over 73 as he mixed a birdie at the 13th with bogeys at the 10th and 18th.

After slipping to three-over with bogeys at the first and second, he got back to level par with an eagle two at the fourth and a birdie at the sixth before dropping another shot at the par-five ninth.

Thomas bogeyed his first hole, the 10th, but still went out in seven-under 29 as he followed an eagle at the 12th (18ft) by playing the five-hole stretch from the 14th to the 18th in six-under.

After a birdie at the 14th, he chipped in at the 15th and 16th, made a seen footer  17th and another then hit a wedge stone dead from 163 yards to set up his second eagle of the day at the par-five 18th.

He then birdied the third from 10 feet, picked up another shot at the seventh and made a 10 footer for another gain at the ninth for his 63.