Shean O. Wills, 23, and Abigail Torres, 18, were arguing with the woman about 8:20 p.m. at the corner of Broadway and Stonehinge Lane, police said.
At one point, Torres cut the left side of the woman's face with the blade, police said. Torres snatched the victim's cellphone, then left in a car driven by Wills, police said.
The victim, 18, was treated at a hospital for nonlife-threatening injuries, police said.
Later that night, Torres and Wills were arrested at their Wyandanch home, 49 Brooklyn Ave., police said.
Torres was charged with first-degree robbery, first-degree assault and fourth-degree possession of a dangerous weapon. Wills was charged with first-degree robbery and fourth-degree criminal facilitation.
Arraignment details were not immediately available early Thursday evening.