Might be third fastest split ever:
Jarmila Kratochvílová (CZE) ran a 47.6 Split in the 1982 Athens European Championship final, a 47.75 split in the 1983 Helsinki World Championship final, and a 47.9 split in the 1983 Europa Cup in London.
Marita Koch (GDR) ran a 47.70 split in Erfurt 1984, a 47.9 split in the 1982 European Championship final, and a 47.9 split the 1985 Canberra World Cup.
Olga Nazarova and Olga Bryzgina (USSR) both ran a 47.80 split in the 1988 Seoul Olympic final (current world record)
Allyson Felix (USA) ran a 48.01 split in the 2007 Osaka World Championships final, and a 48.20 split in the 2012 London Olympic final.
Florence Griffith-Joyner (USA) ran a 48.08 split in the 1988 Seoul Olympic final.