The Olympic champion, Semenya, accelerated in the last 50m to pass American Ajee Wilson and Burundi's Francine Niyonsaba to win her third world championships gold in the 800m in a new personal best and fastest time this year of 1:55.16.
Niyonsaba, the 2016 World indoor champion, claimed the silver in 1:55.92 as American Wilson took bronze in 1:56.65.
Kenya's 2015 world silver medallist Elijah Manangoi, clocked 3:33.61 to beat his compatriot Timothy Cheruiyot (3:33.39).
Norwegian Filip Ingebrigtsen dived over the finish line to take a surprise third place in 3:34.53 from Spaniard Adel Mechaal, who recorded 3:34.71. Defending champion
Asbel Kiprop over the last 150m faded to ninth place.
Kenya's Hellen Obiri beat Almaz Ayana, the double Olympic champion from Ethiopia, into second place with a time of 14:34.86. Netherland's Sifan Hassan of the concluded the women's 5000m podium in 14:42.73.