Kenya's Olympic champion Faith Kipyegon took one step closer to upgrading her world silver medal from 2015 to gold after winning the first semi-final in 4:03.54.
Just as she had done in the heat, Great Britain's Jessica Judd led the field through 400m in 65.11 and through 800m in 2:11.84. Dibaba was well-positioned on the young Briton's shoulder, with South Africa's Olympic 800m champion Caster Semenya and Great Britain's British record-holder Laura Muir running comfortably mid-pack. As they approached the bell in 3:01.33, Muir came wide to position herself on Kipyegon's shoulder alongside Dibaba. With 200m to go, 2009 world 800m champion Semenya – something of a dark horse over 1500m – showed some of her 1:55.27 two-lap speed as she moved up to join the leaders.
As the leaders approached the homestraight, it was clear that Dibaba was treading water. Meanwhile Kipyegon, Muir (4:03.64) and Semenya (4:03.80) finished full of running, showing that they could all be forces to be reckoned with in the final on Monday evening.
Poland's Angelika Chichocka, who won the IAAF Diamond League Meeting in Rabat, and Germany's Hanna Klein bagged the other two automatic qualifying spots with 4:03.96 and 4:04.45 respectively. Dibaba ultimately took one of the non-automatic qualifying spots with 4:05.33 in sixth, along with Morocco's Rababe Arafi (4:05.75).
The second semi-final started much slower, with Great Britain's 2014 European bronze medallist Laura Weightman leading the field through 400m in 67.17. The field was still bunched together through 700m, when Germany's European U23 champion Konstanze Klosterhalfen put in a surge, immediately opening a gap on the rest of the field, as she passed 800m in 2:15.34.
However, world indoor champion Sifan Hassan – the fastest in the world this year – and Sweden's 2014 European champion Meraf Bahta, passed the young German on the backstraight, followed by Kenya's 2006 world U20 and 2005 world U18 silver medallist Winny Chebet and Weightman. Hassan took victory in 4:03.77 from Bahta's 4:04.04, with both athletes looking like they have more in reserve for the final.
US champion Jenny Simpson came through strongly on the homestraight to take third spot, as she aims to win her third world 1500m medal after her gold in 2011 and silver in 2013. Weightman and Moroccan Malika Akkaoui secured their place in the final as automatic qualifiers in fourth and fifth.
Klosterhalfen suffered for her injection of pace, eventually winding up eighth, whilst 3:59.47 runner Besu Sado of Ethiopia also failed to qualify for the final - IAAF