Usain Bolt wins men 's 200m gold to complete historic sprint double . Score: 6 Rudisha takes gold in one minute 40.91 seconds . Caster Semenya qualifies fastest for women 's 800m final .
Usain Bolt wins men 's 200m gold to complete historic sprint double . David Rudisha of Kenya breaks his own world record in the men 's 800m . Rudisha takes gold in one minute 40.91 seconds . Caster Semenya qualifies fastest for women 's 800m final .