Kate Anderson and Brooke Halliday looked to form a new stand, Anderson looking in strong form.
Needing a breakthrough, Lili'i turned to Armstrong who delivered once more. Barnett got under the catch to dismiss Halliday before Jesse Prasad marked her return to domestic cricket with Anderson's wicket after a fast 29.
Prasad ensured the Hearts kept the pressure on as Spirit's good start fell away, all out for 193 in 46.1 overs despite a gutsy 32 from youngster Olivia Lobb - while Armstrong finished with an outstanding 4-18 off her eight overs and Barnett 3-55.
The Hearts didn't get the strong start with the bat that they no doubt desired, both Saachi Shahri and Izzy Gaze back in the pavilion at 19/2, Richardson and Lily Mulivai in the action early for the visitors.
The Hearts missing their WHITE FERNS contingent, now Arlene Kelly's experience was needed to steady the ship under early pressure, and she reached 37 in a 63-stand with her captain before offering a return grab to Charlotte Sarsfield.
Lili'i lost a further two partners but was still in charge with 10 overs to go, needing 51 more runs with Tariel Lamb in support.
She would reach a career-best 63 in her 50th List A match - but it was chastened by the loss of her wicket at the end of the 46th, at a crucial moment for her side.
The Spirit kept attacking, while the Hearts needed 16 runs from the last two overs. But instead of the boundaries flowing, wickets were falling in a flurry - Richardson striking twice in the 49th over to give Spirit the edge.
Thirteen needed from Caroline Esterhuizen's final over now. Nailbiter! With seven runs from the first five balls, Amie Hucker was left needing a sixoff the final delivery. It wasn’t to be with Hucker bowled trying to power the ball over the legside.
In their breakthrough summer, Spirit had done it - secured the home Grand Final (venue to be confirmed) to be played Saturday March 14. Meanwhile, Canterbury hearts were breaking in New Plymouth where a special captain's century wasn't quite enough to push them past the Hearts on the table. It would be a rematch in three weeks' time: Northern Spirit and the Auckland Hearts fighting for the Hallyburton Johnstone Shield.