The fastest woman of 2014, the USA's Francena McCorory, flew to the fastest time of the semi-finals wiith a swift 51.35 clocking.
The 25-year-old comfortably claimed the second heat, which was significantly quicker than the first, as the US champion and 50.85 sprinter enters tomorrow’s final as the favourite for the gold medal.
Behind her, Jamaica’s Kaliese Spencer, who is better known as a hurdler, registered a 51.58 lifetime best to assert her intentions for a global medal without the barriers.
Former world junior and world youth champion Shaunae Miller ran a 51.63 season’s best for third position in the same race, by far the faster of the two semi-finals.
Jamaica’s Patricia Hall took the first, and slower, heat with a 52.82 clocking ahead of Poland's Justyna Sweity whose 52.97 run into the two-lap final whipped the home crowd into an excitable frenzy.
Lisanne De Witte of the Netherlands initially took the final qualification spot in third place but was later disqualified after the Jury of Appeal accepted the US team’s argument that she had impeded Joanna Atkins and the latter eventually progressed to Saturday’s final.
Among those to miss out on a spot in the final was Russia’s Kseniya Ryzhova, the fastest European this winter, who finished fourth in the second heat with 51.64, just 0.01 outside a qualifying spot and more than a second quicker than the other semi-final winner Hall.
Czech Republic’s Denisa Rosolova failed to finish the first heat after colliding with De Witte, while Nigeria’s Regina George, the fastest in the first round, failed to present herself for her semi-final.
Nicola Bamford for the IAAF