In a men's singles third-round match, the Thai ace edged out Malaysia's Muhammad Roslim Hashim - the winner here in 2001 - by 21-18 21-18.

"Today, I think the match was 50-50," said the Thai fifth seed.

"He made a mistake twice in a row at 18-all to go 20-18, I think that decided the match," added Boonsak, who has now won his last four matches against the Malaysian.

Countryman Poompat Sapkulchananart went down to Danish world No 4 Peter Gade 21-17 21-14.

Three other Thais also bowed out in the women's singles second round. World No 28 Soratja Chansrisukot lost 21-18 17-21 21-9 to Xing Aiying from Singapore.

Boonsak's sister, Salakjit, fell to Japan's Mizuki Fujii 21-18 21-17, while Monthila Meemek was crushed by another Japanese, Nozomi Kametani, 21-13 21-17.

In the women's doubles, Thailand's Duand-Anong Aroonkesorn and Kulchala Vorvichitchaikul, who are ranked 19 in the world, suffered a 21-14 21-17 loss to world sixth-ranked Chien Yu-chin and Cheng Wen-hsing from Taiwan in the second round.

Meanwhile, world No 10 Boonsak will meet world No 2 Lee Chong-wei in the quarter-finals. The Thai has never beaten the Malaysian in three previous meetings. Their most notable encounter was in the final of the Asian Championships in April, when Lee dashed Boonsak's hopes of winning the title with a clinical 21-12 21-16 annihilation.

"I've lost to him three times, I want to beat him this time. I'll try my best," said Boonsak.

In the mixed doubles second round, world No 4s Sudket Prapakamol and Saralee Thungthongkam also reached the quarter-finals, where they meet Danes Jens Eriksen and Lena Frier Kristiansen after beating Taiwan's Tsai Chia-hsin and Cheng Wen-hsing 25-23 14-21 22-20 in the second round.

World No 8s Saralee and Sathinee Chankrachangwong also progressed and face China's world fifth-ranked Wei Yili and Zhang Yawen. The Thai pair thrashed Japanese qualifiers Fu Jii and Kakiwa Reika 21-13 21-13 in the second round.