Olympic champions USA took to the track with confidence in the opening round of the 4x100m, and they raced with grace and precision as well as they dominated the round on Thomas A Robinson's soggy track.
Once again it was Tianna Bartoletta, the lead runner at the previous two editions, who got things off, passing to Jenna Prandini who increased their margin midway through the back stretch. Olympic finalist English Gardner all but sealed the win with a strong performance around the final bend, before handing off to Morolake Akinosun to forged on to a 42.96 victory, more than 10 metres clear of runners-up China who clocked 43.98.
The Netherlands, with world 200m champion Dafne Schippers on the second leg, seemed to struggle mid-race, but came back to finish third in 43.98 to nab the third automatic qualifier to this evening's final.
Heat two produced a surprise with Germany nabbing an upset victory over defending champions Jamaica. Running virtually even after the final exchange, Rebekka Haase steadily pulled away from Jamaican anchor Christania Williams to confidently cross the line unchallenged in 43.04. Jamaica, who included Simone Facey, Natasha Morrison and Gayon Evans in legs one, two and three, clocked 43.22 to easily move on to this evening's final as well.
Further back, France finished third in 44.14 to move on, with Brazil (44.20) also advancing on time.
The Bahamas, fourth in the first heat in 44.11, also moved on to the final.
Bob Ramsak for the IAAF