Fifth seed Chen Long of China tumbled out of the World badminton championships on day one, beaten by little-known Kevin Cordon of Guatemala, at Wembley Arena on Monday.
In a 74-minute thriller, world number 36 Cordon clinched victory on his fourth match point 21-19, 8-21, 27-25.
"It's the biggest win in my life by far," a delighted Cordon told reporters.
"Since March I have been training in Spain with the national team so that has been good."
Chen, 22, who also had three match points, said: "I never thought I would lose."
Top seed Lee Chong Wei started his bid for a maiden world title with a 21-15, 21-17 success over Thailand's Tanongsak Saensomboonsuk.
The Malaysian world number one was made to work hard by the gritty Thai who took five points in a row in the second game to lead 11-8.
But Chong Wei, aided by some deceptive returns of serve, regained control to move safely into the second round.
"I didn't play very well and made a few mistakes," he said. "It sometimes happens in the first round."
Former world and Olympic champion Taufik Hidayat, the other big name on parade at the Wembley Arena on the first morning, was level 6-6 in the opening game with Peru's Rodrigo Pacheco Carrillo.
The Indonesian, though, pressed on to lead 15-7 before clinching a 21-10, 21-14 victory.
Holder Chen Jin breezed past Estonia's Raul Must 21-8, 21-10.
Olympic champion Lin Dan, seeking a fourth world crown, faces Kestutis Navickas in his first match on Tuesday.
