A stunning result in the women's 4x100m relay heat saw the favored American team drop the baton on an exchange and finish in last place, failing to qualify for the finals.
The reigning Olympic gold medalists botched the exchange between the second and third legs, as Allyson Felix dropped the baton as she was passing it off to English Gardner.
Gardner would eventually pick up the baton, and the U.S. would finish the race well behind the rest of the field. After further review, it appeared the Brazilian racer waiting to accept the baton in the adjacent lane made contact with Felix, causing her to stumble and drop the baton.
The Americans have since filed a protest alleging interference, with a decision expected later in the day.