London - Azeri-born Turk Ramil Guliyev ruined Wayde van Niekerk's bid for a first 200m/400m double in 22 years when he outsprinted the South African to the 200m world title on Thursday.
Guliyev, who took up Turkish citizenship in 2011 and was cleared to compete for his adopted country two years later, clocked 20.09 seconds, with Van Niekerk adding silver to the 400m gold medal he won on Tuesday.
Jereem Richards of Trinidad and Tobago claimed bronze in a photo finish from the South African.
"It's not a shock," insisted the 27-year-old Guliyev, who was draped in both Azeri and Turkish flags.
"I wanted to win and this year I thought it was possible and I made it. I believed in myself."
There were a few boos from the packed-out London Stadium crowd as Guliyev streaked through the line ahead of Van Niekerk, thousands immediately upping and leaving rather than savouring the winning moment which ruined the South African's bid to match Michael Johnson, the US track legend who won the double at the 1995 Gothenburg worlds and went on to repeat the feat a year later in the Atlanta Olympics.
With Usain Bolt, winner of the last four world titles, opting not to race the distance in his swansong season, the competition was lined up for a duel between Van Niekerk and Botswana's Isaac Makwala, the fastest sprinter over 200m this season.
The Botswanan rebounded from an IAAF ban on him competing in the 400m as he was placed under 48-hour quarantine in a bid to contain the highly contagious norovirus bug which has affected some athletes' hotels.
Makwala was forced to run an additional solo 200m qualifying time-trial before Wednesday's semi-finals and that extra exertion seemed to have taken its toll as the 30-year-old came in sixth (20.44).
IAAF World Championships finals results on Thursday:
1. Ramil Guliyev (TUR) 20.09 seconds
2. Wayde van Niekerk (RSA) 20.11
3. Jereem Richards (TTO) 20.11
4. Nethaneel Mitchell-Blake (GBR) 20.24
5. Ameer Webb (USA) 20.26
6. Isaac Makwala (BOT) 20.44
7. Abdul Hakim Sani Brown (JPN) 20.63
8. Isiah Young (USA) 20.64
1. Christian Taylor (USA) 17.68 metres
2. Will Claye (USA) 17.63
3. Nelson Evora (POR) 17.19
4. Cristian Napoles (CUB) 17.16
5. Alexis Copello (AZE) 17.16
6. Chris Benard (USA) 17.16
7. Andy Diaz (CUB) 17.13
8. Jean-Marc Pontvianne (FRA) 16.79
1. Kori Carter (USA) 53.07 seconds
2. Dalilah Muahammad (USA) 53.50
3. Ristananna Tracey (JAM) 53.74
4. Zuzana Hejnova (CZE) 54.20
5. Lea Sprunger (SUI) 54.59
6. Sage Watson (CAN) 54.92
7. Cassandra Tate (USA) 55.43
8. Eilidh Doyle (GBR) 55.71