Grimaldi jumped 5.76m to claim gold by 9cm from Russian Paralympic Committee jumper Aleksandra Moguchaia.
It completes a five-year cycle in which the 24-year-old contended with a stress fracture in her foot for 18 months in 2017 and 2018.
Grimaldi made an early statement on a wet track when she opened with a jump of 5.74m, eclipsing the previous Paralympic record by 3cm.
It was also 12cm further than her winning jump in Rio in 2016.
Moguchaia and Ecuador's Kiara Rodriguez, who won bronze, both delivered handy responses.
However, neither could haul in Grimaldi's distance.
She added 2cm to her distance on her fourth jump, finishing with three of the competition's four best jumps.
Fellow Dunedin Paralympian Holly Robinson is in action at 10.28pm tonight in the F46 javelin.
