China's Olympic champion Chen Long was dumped out of the All-England Open on Thursday, losing in the second round to Tanongsak Saensomboonsuk, the world number 12 from Thailand, 21-16, 21-19.
Seven months and an absence of competition made Chen vulnerable and so did Tanongsak's sensible strategy of not too frequently attacking an opponent who creates brick-wall mid-court defence and turns it into damaging counter-attack.
Chen fought hard to close a five-point deficit to 19-19 in the second game, and might well have improved had the match gone to a decider.
Instead on the next point he hurtled a smashed wide, and then lifted the shuttle a little too short to defend against Tanongsak's attack on match point.
"Every player wants to win this title and I did too," said 28-year-old Chen. "My ambition is to get back my form."
The upset could help Lee Chong Wei, the top-seeded three times former champion from Malaysia, who survived for the second day with an ailing knee and who might now meet Tanongsak in the semis.
Lee again proved himself once again a master of adaptability and economy while enduring the discomfort of his knee injury and overcoming Wang Tzu Wei, a young and ambitious world number 21 from Taiwan, en route to the quarter-finals.
Lee defended economically, controlled most of the rallies at a pace at which he felt comfortable, and mixed up the patterns cleverly as he squeezed through 21-18, 21-18.
"I just tried to forget my injury," the world number one said, when asked what he had been trying to do.
One hour after Chen's defeat, the other Olympic singles champion almost followed him to the exit.
Carolina Marin was within two points of defeat at 17-19 in the second game against He Bingjiao, a 19-year-old left-hander who looks like China's next great women's singles hope, before surviving 15-21, 21-19, 21-10.
Marin next plays Ratchanok Intanon, the former world champion from Thailand, while the top seeded Tai Tzu Ying saved three game points in a 27-25, 21-11 win over Minatsu Mitani of Japan and faces Pusarla Sindhu, the Olympic silver medallist.
The other Indian, Saina Nehwal also reached the last eight, despite an ongoing recovery from a knee operation.
So did Lin Dan, the three-time Olympic champion and men's titleholder, who moved well enough during a 21-16, 21-11 win over compatriot Huang Yuxiang, and kept alive sentimental hopes of a Lee-Lin farewell in Sunday's showdown.
Lin next plays Viktor Axelsen, the World Super Series champion from Denmark, who overcame Zhao Junpeng of China, 21-10, 21-11.
Ng Ka Long, the eighth seed from Hong Kong, was beaten 21-16, 21-14 by Shi Yuqi, the 21-year-old world number 10 from China, while Jan Jorgensen, the second seeded Dane, was beaten 21-16, 21-13 by Kazumasa Sakai, the world number 53 from Japan.