Emmanuel Korir led home countryman Ferguson Rotich to complete a Kenyan one-two in the 800m final.
Korir, who finished sixth in the 400m final at Doha 2019, showed his finishing speed as he made a decisive break for home around the final bend and came home in 1:45.06.
Rotich, the fastest into the final had to settle for silver ahead of Poland's Patryk Dobek.
American world champion Donavan Brazier was absent after failing to qualify from the American trials while Botswana's Nijel Amos, the fastest man in the world this year, was well back in seventh.
Kenya has won the men's 800m at the last four Olympics with Wilfred Bungei's success at Beijing followed by London and Rio titles for the great David Rudisha, who is still only 32 but has not raced since 2017 after a series of injuries.
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