IMO the greatest upsets are: - Kevin Cordon defeated Chen Long (21-19, 8-21, 27-25) in WC 2011 1st round - Petra Overzier defeated Jiang Yanjiao (21-18, 14-21, 21-14) in WC 2006 quarterfinal - Muhammad Hafiz Hashim defeated Chen Hong (17-14, 15-10) in All England 2003 Final - Park Sung-hwan defeated Lin Dan (21-13, 21-13) in WC 2010 quarterfinal What about yours?
Brice Leverdez knocking out LCW from the WC quite recently. LCW wasn't exactly playing on top form, but neither was he expected to have a R1 exit...
biggest upset in history? Ronald Susilo defeated Lin Dan in 2004 Athens Olympics, 1st round, in straight sets. I cannot imagine any upset more signifcant than that. In the most significant arena for badminton, Lin Dan was at the top of his form, he was ranked number 1 in the world, he was expected to podium if not outright win it, but at the first round, defeated by a much lower ranked player from Singapore.
Tian Houwei beating Lee Chong Wei at the 2013 Australian Open was pretty impressive. Their rankings were something like 1st vs. 140th
Another vote for Lin Dan losing in Athens 2004. Also, as I was there to see it live; Lee Chong Wei losing to Sai Praneeth at the 2016 All England first round (24-22, 22-20). I was there and watched in awe as LCW had control for the first 11 or so points then managed to throw away the lead and game. Then the second game with the same errors again. I went along expecting LCW to win the tournament and set himself up as favourite for Rio. It was surreal to see loads of people looking around wondering what just happened.
My coach beating the no.1 seed in 2001 World Championships Mens singles in the 2nd round. We were like saying to ourselves "he did what????" Pity he lost the next match to the eventual gold medallist.