Neighbours ran out of their homes to scare off the two male muggers who ambushed the woman, in her 40s, as she walked home at 11.10am on New Year’s Eve.
The victim reached out to witnesses on social media and thanked passing motorists and residents for coming to “save her”.
There were no reports of any injuries in the knifepoint attack.
A Met spokesman said: “Police are investigating after a woman in her 40s had a knife held to her throat on Robin Hood Lane in Sutton.
“The incident happened at around 11:10hrs on Saturday, 31 December as the woman was grabbed from behind.
“She screamed which caused passing cars to stop and the two male suspects made off.”
The force added there have been no arrests so far.
Any witnesses or anyone with information is asked to contact 101 quoting reference 2973/31Dec.