Unheralded Thai Udorn Duangdecha carded an eight-under-par 62 to claim a one-stroke lead at the UBS Hong Kong Open.

Despite battling a fever, Udorn missed out on equalling the course record only after finishing his round with a second bogey of the day following a three-putt on the already testing ninth green in torrential rain and fading light.

Two-time European Tour winner Robert-Jan Derksen had set the pace in the morning with a seven-under-par 63.

Udorn, 39, is enjoying his best season on the Asian Tour after doubling his lifetime earnings with a career-best second-place finish at August's Queen's Cup in his native Thailand before claiming third at last month's Mercuries Taiwan Masters after leading for the first three rounds.

"I am not surprised by how I played because I followed my gameplan," said the Chang Mai native, who turned pro in 2000.

"Last year my preparations were not very good but this year I have a better feeling. My body is in a better shape and I have had better practice."

Former Dutch Amateur champion Derksen, who last tasted victory at the 2005 Madeira Island Open, finished with a flourish at Hong Kong Golf Club, with five birdies and the only bogey of his round over his last six holes.

"It was very good. I didn't hit many bad shots, just one three-putt at 16," said the 2003 Dubai Desert Classic champion.

"I hit almost all the greens and fairways to give myself chances and I putted beautifully."

Asian Tour Order of Merit leader Thongchai Jaidee, a two-time European Tour winner this season, sits two off the pace alongside defending champion Lin Wen-tang, David Dixon and Gregory Bourdy at six under par.

Former Open champion Ben Curtis, Mark Foster, Indian Masters champion SSP Chowrasia and South African duo Rory Sabbatini and Charl Schwartzel are in a group three shots off the pace.

Race to Dubai leader Lee Westwood and nearest challenger Rory McIlroy sit together at four under in a group including Mark O'Meara and China's Liang Wen-chong, who trails Thongchai in the battle to become Asian number one.

Westwood leads McIlroy by a mere 52,321 euros at the top of the European money list, with Hong Kong representing the last event ahead of the season-ending Dubai World Championship.

"I am happy with 66. I could have let it get away from me on the front nine, my back nine, but it is okay," said last year's runner-up McIlroy.

"I am in a good position but there is still a lot of golf left to play so it was nice to get off to a good start."

Despite struggling with the grain of the putting surfaces during his first competitive trip around the tight tree-lined course, Westwood hit 17 out of 18 greens as the Portugal Masters champion shipped only two bogeys.

"It was good, the only green I missed was the last hole I played and it is a tough green at number nine. I had a lot of chances," said Westwood.

"The greens are puzzling, I think I am at a disadvantage having only played the course once before.

"It is pretty obvious tee to green but there is a big advantage having played a few tournaments around here so, to start with a 66, I am delighted because the only two bogeys I made were three-putts and I missed a lot of chances."

Meanwhile, Jean-Francois Lucquin's hole-in-one at the start of his one-under-par first round earned local charity Operation Santa Claus US dollars 10,000 from tournament sponsors UBS.