The United States won the men's 4x400m gold, with Great Britain just missing out on a medal in a tight finish.
Members of the USA 4x400m relay team celebrate
The Americans, seeking to atone for the shock defeat of their 4x100m team, sped home in two minutes 55.91 seconds with Australia winning a surprise silver.
Britain's team of Tim Benjamin, Sean Baldock, Malachi Davis and Matt Elias were in bronze position going into the final 100m of the race.
But Nigeria and Japan both overtook Elias in a desperately close finale.
Benjamin, who gave Britain a great start, was devastated that their season's best time of 3:01.07 was not good enough to see them secure a medal.
He said: "I ran my heart out. I think only the Americans took me out - it was one of my fastest runs this year.
"I am gutted we couldn't get a medal. I thought we had done enough."
The outstanding American team of Otis Harris, Derrick Brew, indiviudal 400m champion Jeremy Wariner and Darold Williamson won by almost five seconds from the Americans.