No surprises emerged from a competitive opening round, with defending champions USA, and perennial powers Jamaica and Poland looking the strongest ahead of tomorrow evening's final.
After running close with Australia over the opening two laps in heat one, world leader Quanera Hayes took command for the US quartet with a 50.73 split, the second fastest of the round. That allowed Natasha Hastings to come home on cruise control to seal the 3:29.27 win, the fastest of the three heats.
Stringing together a consistent series of 52-second legs, Australia finished a strong runner-up in 3:30.31 to also advance.
The second heat brought the crowd to life as Shaunae Miller-Uibo, the host country's biggest sporting star, led the Bahamian quartet on to the track – and again several minutes later when she was formally introduced, and again a minute after that when the Olympic champion led off for the hosts.
Running in lane seven, Miller-Uibo made up the stagger on Canadian Carline Muir after 250 metres, giving her squad a three-stride lead after an impressive 50.25 leg, the fastest of the evening. They held their lead through legs two and three but the pressure was too much for anchor Rashan Brown, who eventually faded to fourth and out of contention for a spot in the final.
The race for the win came down to Great Britain and Nigeria with Margaret Bamgbose out-dueling Briton Kelly Massey over the waning stages to take the victory in 3:31.97. The British squad were next in 3:33.00 to move on as well.
Poland produced the most entertaining victory of the round, battling with Jamaica leg-for-leg, with anchor Justyna Swiety even tossing in an impressive come-from-behind flourish to overtake Anneisha McLaughlin-Whilby over the final 40 metres. Poland clocked 3:29.42 and Jamaica 3:29.93 to easily claim their spots in the final.
Botswana was next in 3:31.61 with Germany fourth in 3:34.34 to take the last two lanes in the final.
Bob Ramsak for the IAAF