Just as has been the case in four of the past five IAAF World Championships, the battle for gold looks likely to be between the USA and Jamaica.
The two 4x400m relay powerhouses each won their respective heats, but the USA will start tomorrow's final as favourites having clocked a world-leading time of 3:21.66 when winning heat one, whilst Jamaica took heat two in 3:23.66.
US champion Quanera Hayes got the US quartet off to a good start, clocking 49.92 on leg one to establish a big lead after the opening 400m. Although Kendell Ellis lost a bit of ground on leg two (51.59), NCAA silver medallist Shakima Wimbley stormed further away from Great Britain's Perri Shakes-Drayton on the third leg with the fastest time of 49.20 and it was just left to experienced relay runner Natasha Hastings to bring the team home after a 50.20 split.
"To come out with a world lead, I certainly wasn't expecting to run that fast in round one. Maybe we're going to come out the final tomorrow and do something really special and make some magic happen. But we are Team USA so they're all gunning for us,” explained Hastings.
If the USA take gold from their Caribbean rivals, the finishing order of the top two will be a repeat from the IAAF World Championships in 2007 in Osaka, 2009 in Berlin and 2011 in Daegu. Two years ago in Beijing, Jamaica reversed the order when Novlene Williams-Mills overtook Francena McCorory in the closing metres, but the USA made no mistake in the Rio Olympics last year, re-gaining pole position and here at the IAAF World Championships London 2017, they look poised to retain their top spot.
The USA – winners of this event at the IAAF World Relays Bahamas 2017 earlier this year – will also have the option of bringing in some big names for the final. Newly crowned world 400m champion Phyllis Francis and 2017 world bronze medallist Allyson Felix – the latter hoping to add to her 14 IAAF World Championships medals by also getting on the podium in the relays – will likely boost the US squad in the final.
The race for bronze looks likely to be open. Great Britain took bronze at the Olympic Games last year and here in London they were third fastest qualifiers after finishing second to the USA in heat one. Interestingly, their 3:24.74 clocking was over one second quicker than their time for bronze in Rio last year.
However, the home nation will have a fight on their hands. Botswana are improving and clocked a national record of 3:26.90 for third in the same heat. Nigeria - who have never finished higher than fifth in this event at the IAAF World Championships - also emerged as a potential medal contender, after clocking a controlled 3:25.40 for second in heat two behind Jamaica.
Germany took third in heat two to qualify for the final, whilst Poland – second in the IAAF World Relays in April behind the USA – were fourth to also secure their place.
Behind Botswana in heat one, France qualified as the eighth team for the final.
Emily Moss for the IAAF