Kenya's Margaret Wambui, bronze medallist at both the world indoors and Olympics a year ago, won that heat, but Arzamasova's season's best of 2:01.92 was not fast enough to see her bag one of the faster loser places.
First Wilson and then Niyonsaba took the fight to the South African, going out quickly on the first lap as Semenya settled into her usual position in the middle of the pack.
The race got off to a fairly quick start, and unsurprisingly it was natural front-runners Niyonsaba and Wilson who went straight to the front, with Semenya, Wambui, and Sharp sitting comfortably behind them.
The 26-year-old South African was one of a number of women taking medication to lower her testosterone level until 2015 when the Court of Arbitration for Sport (CAS) suspended an IAAF rule that enforced a limit on naturally occurring levels.
Semenya, a bronze medallist in the 1500m in London as she attempted an audacious double, clocked an impressive 1min 58.90sec, looking incredibly comfortable as she broke with 20 metres to run.
Semenya, who stands to be awarded the 2012 Olympic gold medal after Russian victor Mariya Savinova was disqualified for doping, now has to await further meetings between the IAAF and CAS to discover if she again has to take testosterone suppressing medication.