Felix ran an outstanding second lap, clocked at a startling 48.7sec, as the quartet, also comprising Quanera Hayes, Shakima Wimbley...
Felix ran an outstanding second lap, clocked at a startling 48.7sec, as the quartet, also comprising Quanera Hayes, Shakima Wimbley and newly-crowned 400m champion Phyllis Francis, timed 3min 19.02.
Britain, in 3:25.00, held off Poland (3:25.41) for silver.
Jamaica's sprinting woes continued as their foursome failed to make it around after Anneisha McLaughlin-Whilby pulled up on the second leg and had to be taken off the track in a wheelchair.
Felix's gold in the shorter relay on Saturday saw her overtake Jamaicans Merlene Ottey and Usain Bolt as the record world medal holder.
The 31-year-old also won a bronze in the 400m and of her 16 world medals, 11 have been gold, while nine in total were won as part of the US relay team and seven individually.
Felix has also bagged an incredible nine Olympic medals including six gold.
"It does mean so much to me every time," Felix said when asked whether medals motivated her.
"I love this sport. I'm grateful to run with these amazing girls. They work so hard and deserve all their success.
"It's an honour to run in the relay for Team USA and I will always treasure these moments."
Felix kicked off her incredible medal haul with a 200m silver medal at the 2004 Olympics in Athens, her first global gold coming in the 200m at the Helsinki world champs a year later.