With Chellaston hot favourites because of the way they had won the league, Diamonds could have been overwhelmed by this cup final.
However, a superb free kick from Jade Lambeth gave Diamonds a half-time lead.
Chellaston came out all guns blazing after the interval, and were awarded a penalty for a handball which was converted to make it 1-1.
With chances coming at both ends, it was the defence that kept the tie at stalemate. A superb double save from Elsie Baxter right at the death meant the game went into extra time, and onto penalties.
Chellaston only managed to convert two out of their five, as Baxter pulled off two fantastic saves and Diamonds hit the net three times to claim the cup.
Girls aged six to 16 interested in joining the Diamonds should call 01543 254 069.