Turkey's Guliyev finished first in a time of 20.09 with 400m winner Van Niekerk second on 20.11 and Jereem Richards third in the same time.
There was no fairytale finale for Isaac Makwala of Botswana, who finished sixth having been deemed unfit to run the 400m final on Monday by the IAAF due to illness.
Great Britain's poor run of results at the Championships continued with Mitchell-Blake finishing fourth as another medal slipped away for the home team.
Guliyev, representing Turkey after switching allegience from Azerbaijan, had never won a medal in a senior global event, finished just the stronger to triumph in 20.09 seconds before setting off on a lap of honour carrying the flags of both his nations.
South African Van Niekerk, who took the 400m title on Tuesday, had been seeking to match American Michael Johnson's achievment of doing the 200/400m double but had to settle for silver.
Richards of Trinidad and Tobago was given the same time but was relegated to third by one thousandth of a second.
Makwala, the crowd favourite after his illness travails this week, started strongly but faded to sixth.