By Mitch Phillips
RIO DE JANEIRO (Reuters) - Five-times defending champions the United States and Jamaica, who upset them at last year's world championships, set up what should be a mouth-watering women's Olympic 4x400 relay final after impressive semi-final performances on Friday.
Both teams rested key athletes ahead of Saturday's final, aware that their strength-in-depth meant there was no danger of missing out providing there were no baton mishaps.
The Americans, who last missed out on gold in 1992, won the first heat by a distance in three minutes 21.42 seconds and Jamaica nearly matched them in the second with 3:22.38.
Ukraine, Britain, Canada, Italy, Poland and Australia also advanced for what is likely to be a race within a race for bronze.
France and the Bahamas, who set a national record, missed out.
(Editing by Ed Osmond)