American Bershawn Jackson powered his way through heavy rain to 400m hurdles world gold after defending champion Felix Sanchez failed to finish. Sanchez, bidding for a third successive global title, pulled up clutching his right hamstring after the first hurdle.
Jackson, 22, produced a personal best 47.30 seconds to edge compatriot James Carter, who also clocked a personal best time of 47.30 secs in Helsinki.
Dai Tamesue of Japan held off American Kerron Clement to take bronze in 48.10.
"I went out and tried to keep my composure and keep strong," said Jackson, who was congratulated by former world champion Ed Moses after the race.
"Some of the greatest athletes were behind me so I was just wishing I could come round the turn at the same time as them and stay strong."
It was a first major medal for Jackson, who is easily recognisable on the track by his distinctive head band which he wears in memory of his uncle Richard who encouraged his career in athletics.
But, for Olympic champion Sanchez, it was the end of a miserable season during which he has struggled with a foot injury.
The 27-year-old from the Dominican Republic clearly arrived at the championships out of sorts and - after only managing to qualifying as a fastest loser - he false-started in the final before disaster struck.
MMIX
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Well done to Jackson -a great time in such conditions
