* Kiradech defies thyroid problem, leads at seven-under
* Donald struggles in heat, cards 74 (Updates after round is suspended)
March 21 (Reuters) - Luke Donald's Malaysian Open debut got off to a feeble start on Thursday with the world number three, the biggest name in the $2.75 million European Tour event, carding an opening round two-over-par 74 in Kuala Lumpur.
Big-hitting Thai Kiradech Aphibarnrat, battling a thyroid problem, sank four birdies on each nine for a seven-under-par 65 to grab the lead before lightning forced an early end to play.
Donald arrived from the U.S. on Tuesday morning following his tied fourth place finish in last week's Tampa Bay Championship and playing his back nine first, struggled in the heat at the Kuala Lumpur Golf and Country Club.
"It was hard work, I got off to a very slow start," said the Briton, who parred his first hole before a hat-trick of bogeys put him on the back foot at the Asian Tour co-sanctioned event.
The seven-time winner in Europe responded with three birdies on the front nine but could not keep the stretch blemish-free, dropping two shots on the par-four second.
"I think if you are a little bit off on this course it can eat you up at places and I wasn't quite in control and when I did have opportunities I wasn't able to make them on the greens."
Three-time major winner Padraig Harrington made a strong start with a three-under-par 69 while Frenchman Gregory Bourdy birdied five of his first seven holes en route to a six-under-par 66. A score later matched by Italy's Edoardo Molinari and Dane Anders Hansen.
Kiradech bettered them all, despite the ailment which necessitated holding back from blasting his tee shots to preserve energy.
"The weather is too hot and the thyroid disease is making me feel tired," said the 23-year-old Thai seeking his maiden European Tour victory.
Starting on back nine, Aphibarnrat turned in 33, reeled off three birdies in a row from the third and signed off by picking up another shot at his last.
"Honestly, I didn't have enough energy to hit long drives. I'm still taking medication for my thyroid condition and I'll consider going for operation when I consult my doctor in six months," Kiradech told reporters.
Former Masters champion Charl Schwartzel shone in the truncated afternoon session with birdies on the third and fourth before he eagled the long fifth to turn in a four-under 32.
Briton Scott Jamieson matched Schwartzel's outward 32 and eagled the 10th to join the group at six-under before play was suspended.