Kenya's Margaret Wambui, bronze medallist at both the world indoors and Olympics previous year, 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. The South African was fifth going through the bell in a fast pace of 57.98sec.
Niyonsaba herself finished strongly to take the silver medal, with Wilson easing down in the final meters knowing she had secured a medal.
Migrants : des ONG obligées de suspendre les sauvetages en mer
Elle ne veut pas mettre en danger ses équipages après la décision de Tripoli d'interdire aux navires étrangers de naviguer dans ses eaux.
Hitting the home straight, Wilson and Niyonsaba were neck and neck before Semenya moved smoothly outside the lead duo and motored through the line for a convincing victory.
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 has studiously avoided the controversy, instead concentrating on her track performances and she won a bronze in the highly competitive 1500m on Monday in the opening race of her ambitious bid for a distance double.
"Yes, of course", said the two-time world gold medallist Semenya when asked whether she thought she could again medal in the two-lap race.
- Global markets jarred by North Korea fears
- Venezuela could become a risk to US: CIA director
- HubSpot, Inc. (NYSE:HUBS) Shares Bought by State Street Corp
- Watch Out for Fake Eclipse Glasses
- Burning Stock on the move: The Western Union Company (WU)
- BCE appelle à l'égalité dans l'héritage entre les deux sexes
- Odisha swine flu toll rises to six
- Birla Corporation net profit down 54% in Q1
- Météo - Début de journée pluvieux samedi avant des éclaircies l'après-midi
- Arsenal, Leicester all set for Premier League opener