South Americans head-up thrilling day of upsets in Yokohama
Brazil's 4x100m team caused the shock of the 2019 IAAF World Relays.
While all eyes focused on American maestros Michael Rodgers, Justin Gatlin, Isiah Young and Noah Lyles, the South American team of Rodrigo Do Nascimento, Jorge Vides, Derick Silva and Paulo Camilo de Oliveira won the gold medal.
They finished in 38.05 seconds, just 0.02 seconds ahead of the United States, who set a season's best time themselves. An experienced Great Britain team finished third.
In the women's event, U.S.A put to bed their Nassau nightmare from 2016 when a fall on the first leg ended their race, by securing a nail-biting 0.02 second win over Jamaica in the women's 4x100m relay.
Mikiah Brisco, Ashley Henderson, Dezerea Bryant and Aleia Hobbs - all sub-11 100m runners - held their nerve to bring the baton home in 43.27 seconds.
Happy to play underdogs in the run-up, Malgorzata Holub-Kowalik, Iga Baumgart-Witan, Patrycja Wyciszkiewicz and Justyna Swiety-Ersetic would have been quietly confident of their chances.
So it was that the European champions improved upon their second-place finish at the last World Relays in The Bahamas two years ago, clinching gold in 3:27.49, with the much-fancied American's having to settle for second by 0.19 of a second.
It was more woe for the U.S.A in the men's event, with the team being disqualified.
In their absence, reigning world champions Trinidad and Tobago foursome Deon Lendore, Jereem Richards, Asa Guevara and Machel Cedenio secured top spot in 3:00.81
With the mixed 4x400m making its Olympic debut at Tokyo 2020, there was an extra buzz going into this event.
The United States were heavy pre-race favourites on account of their enviable talent pool from which to pick, but question marks hung over the their quartet of My-Lik Kerley, Joanna Atkins, Jasmine Blocker and Dontavius Wright given their lack of international experience.
However the Americans answered any doubters with aplomb, securing a comfortable 1.72 second victory over Canada, with Kenya in third.
The innovative new 2x2x400m made its debut, whereby two athletes take it in turns to run two single laps each.
United States 800m specialists Donovan Brazier and Ce’Aira Brown clocked 3min 36.92sec to bring home the title.
Lokonyen Nathike and James Chiengjiek of the Athlete Refugee Team were seventh in 4:08.80.
The refugee duo competed at Rio 2016 in the 400m and 800m respectively, while Lokonyen also competed at the IAAF World Championships London 2017.
With names like Shericka Jackson, Shashalee Forbes and Elaine Thompson and two-time Olympic 100m champion Shelly-Ann Fraser-Pryce in their ranks, Jamaica were the heavy favourites here.
But a change-over malfunction meant the star-studded team only managed third place, as France's Carolle Zahi, Estelle Raffai, Cynthia Leduc and Maroussia Pare caused another upset to win the gold medal.
United States and South Africa went head-to-head in a thrilling men's event, with the American team of Christopher Belcher, Bryce Robinson, Vernon Norwood and Remontay McClain pipping their counterparts to victory.
This victory secured victory in the only discipline the United States were yet to win at the World Relays.