Birmingham (United Kingdom) (AFP) - Ratchanok Intanon, the youngest ever world singles champion, moved to within one win of a probable All-England Open showdown with Li Xuerui, the Olympic champion, before admitting her patchy form is scary.
The two women battled into the quarter-finals on Thursday, with the 19-year-old Thai coming from behind for the second day in succession and then producing a confessional about her mental state.
At one stage Ratchanok was a game and 11-11 down before getting past Han Li, the world number 19 from China, by 18-21, by 21-14, 21-11.
The day before she was within three points of defeat against the Singaporean Gu Juan.
Honing her survival instincts in this way despite a patchy performance may be crucial, as the seven months since she overcame Li in the world final have, she admits, been hard to handle.
"Everyone has been trying to beat me and I have been putting myself under pressure and been scared of the losses," said the Thai teenager.
"So I try to concentrate on practising. I try not to think about the world championships because I am not the world number one."
That of course is Li, who earlier made a great escape for the second successive day by coming from a game and 8-13 down against Minatsu Mitani, the world number 16 from Japan, also drifting to within three points of defeat before winning 14-21, 21-19, 21-15.
Li had saved a match point on Wednesday against Busanan Ongbumrungpan, the world number 17 from Thailand, and the Chinese player again proved mentally and tactically resourceful as she turned the tide.
"It's a difficult situation when your opponent has a lead," admitted Li. "Both my coach and myself were telling me to keep fighting."
Li next plays Sung Ji-Hyun, the fifth-seeded South Korean who reached the final of the Denmark Open five years ago.
Ratchanok will play Michelle Li, the world number 24 from Canada.
Another to struggle was Saina Nehwal, the seventh-seeded Commonwealth champion from India, who clinched a nervy 24-22, 18-21, 21-19 win over Zhang Beiwen of the United States.
Nehwal sais she had been finding it difficult to sleep because her room was cold. She was, she said, off to look for a heater.
No such movement problems were in evidence for Lee Chong Wei, the men's world number one from Malaysia, who overcame his compatriot Chong Wei Feng 21-6, 21-12, once almost performing a cartwheel on court.
Lee, who hopes to regain the title in what may be his last All-England, now plays a surprise survivor, Kento Momota, the world number 15 from Japan.
Lee's main rival, Chen Long, the second-seeded titleholder from China, resisted a late fight-back by Takuma Ueda, the world number 17 from Japan, to also reach the quarter-finals.
From four points down in the second game Ueda got back to 19-19 and to 20-20 before Chen forced a couple of big smashes through to secure a 21-14, 22-20 win.
The man from Jingzhou now plays Hans-Kristian Vittinghus, the world number 21 from Denmark, whose tenacity eventually helped him squeeze out Boonsak Ponsana, the sixth-seeded Thai, by 18-21, 21-12, 21-19.