London - Ethiopia's defending world champion Genzebe Dibaba was handed a scare in the semi-finals of the 1 500m, but South African Caster Semenya was seamless in her progression.
Dibaba, the world record holder, finished sixth in the first semi, and qualified for Monday's final as one of two fastest times outside the automatic qualifiers.
Semenya, double defending Olympic 800m champion and a two-time world gold medallist in that event, looked very comfortable, producing a trademark kick with a lap to run to keep pace with the race leaders and guarantee the continuation of her audacious bid for a world championships middle-distance double.
Olympic champion Faith Kipyegon of Kenya won the semi in 4min 03.54sec while the Netherlands' world indoor champion Sifan Hassan, who took bronze two years ago in Beijing, claimed the victory in the second semi.
Kipyegon and Hassan have won two Diamond League meetings each this season - the former in Shanghai and Eugene and the latter in Rome and Paris - while Dibaba, who may not be in 3:50.07 world record form of two years ago, has clocked 3:57.82 en route to her 4:16.05 mile victory at the Diamond League meet in Lausanne last month.
Whatever the result, hopes will be high that Monday's 1500 final will not be tainted as the Olympic final in the same stadium at the 2012 London Games.
In that race, six of the top nine athletes have been disqualified for doping violations.
Such was the fallout, the International Olympic Committee has yet to publicly confirm any medal re-allocation, with just Bahrain's Maryam Yusuf Jamal listed in bronze medal position.