Valimaki carded eight birdies in a flawless 64 on Thursday while Simonsen recorded an eagle, seven birdies and a solitary bogey as 82 of the 132-strong field broke par.

"It's a great day," Simonsen said. "I thought it was going to be difficult out there with the wind and it was, but thankfully I played the par fives really well, which helped.

"Most of them were downwind, so that helped a lot, but you still have to hit the shots.

"I haven't played the way I've scored the last two weeks, so it's been very, very frustrating for me. I feel like I've been playing better than what the scores have said. I'll just keep doing what I'm doing and eventually it'll be OK."

Simonsen and Valimaki enjoyed a one-shot lead over German duo Alexander Knappe and Yannik Paul, with home favourite Kiradech Aphibarnrat three shots further back after carding six birdies and a double bogey on the 14th.

The leading Australians were Aaron Pike and Blake Windred, both of whom shot three-under 69s to lie in joint-33rd position, while Louis Dobbelaar and Dimi Papadatos were a shot further adrift, tied for 53rd.