Medal favourite Trayvon Bromell missed out on the final of the men's 100 metres as China's Su Bingtian qualified fastest and Great Britain's Zharnel Hughes won his semi-final.
The Chinese athlete set a new personal best and Asian record after a storming performance in the third semi-final, winning in a time of 9.83.
He was pushed to the line by Ronnie Baker, also setting a lifetime best with the same time as Su, and Marcell Jacobs, whose 9.84 was a European record for the Italian.
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Great Britain's Hughes qualified automatically as he took a surprise win in the second semi-final with a time of 9.98, ahead of Enoch Adegoke of Nigeria. Bromell finished with 10.00 flat in the same heat and was eliminated, to huge surprise.
Bromell's compatriot Fred Kerley, a former 400m runner, edged out Andre De Grasse to take the first semi-final in a time of 9.96, with the Canadian just two one-hundredths of a second slower.
Having earned a reprieve in the first round, a nervy Reece Prescod again false started to play no part in the running of the opening 100m semi.
Bromell had been among the leading contenders to take gold as men's sprinting ushers in a new era at an Olympics without Usain Bolt and Justin Gatlin.
However he looked out of sorts in the heats and could finish only third behind Hughes and Adegoke, the Nigerian dipping more effectively to earn second place by the barest of margins in 10 seconds dead.
The American was then squeezed out of a fastest qualifier's spot as four athletes dipped beneath the ten-second mark in the final semi-final.

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South Africa's Akani Simbine (9.90) was the fourth, and took the second qualifying spot as a fastest loser.
The final appears wide open - any of the eight athletes through will count themselves as realistic medal contenders.

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