17-year-old prodigy Sydney McLaughlin's historic season finally ended in Brazil, as she ran 56.22 in her Olympic 400 hurdles semifinal and was eliminated on time. McLaughlin's junior high school season included a winning anchor leg in the 4x400m at indoor nationals, a 50.9 relay split at outdoor nationals, and a high school, American junior, world youth, and world junior record of 54.15 in the 400 hurdles at the Olympic Trials. She was 16 when she made the Olympic team, making her the youngest American track Olympian since 1972.

Americans Dalilah Muhammad and Ashley Spencer qualified for the final. Muhammad, the world leader, is a heavy favorite for gold. No one ran within 0.66 seconds of her semifinal time. Spencer qualified after clipping a hurdle on the homestretch, falling into third, then bizarrely getting a burst of energy in the last five meters.

In the men's semis, Kerron Clement was the only American man to advance, though he did run the fastest time. Byron Robinson set a new PB of 48.65 seconds and missed making the final by one one-hundredth of a second.

Women's Finalists:
53.89Q Dalilah Muhammad (USA)
54.55Q Zuzana Hejnova (CZE)
54.55Q Sara Slott Petersen (DEN)
54.80Q Ristananna Tracey (JAM)
54.87Q Ashley Spencer (USA)
54.92Q Janieve Russell (JAM)
54.98q Leah Nugent (JAM)
54.99q Eilidh Doyle (GBR)

Men's Finalists:
48.26Q Kerron Clement (USA)
48.32Q Annsert Whyte (JAM)
48.39Q Thomas Barr (IRL)
48.46Q Javier Culson (PUR)
48.49Q Haron Koech (KEN)
48.85Q Boniface Mucheru Tumuti (KEN)
48.61q Yasmani Copello (TUR)
48.64q Rasmus Magi (EST)