Invincibles appear to have every base covered as they hunt a third successive title.
As well as Cox, who brutally flogged anything short over the leg side, opener Will Jacks also hit three sixes in a 27-ball 45.
After both fell, powerful finisher Donovan Ferreira crashed 24 from just nine balls to emphatically seal the win.
While Cox is 63 runs clear at the top of the run-scoring chart, Ferreira has the tournament’s best strike-rate.
Batting is their stronger suit, but the variety of their pace attack always gives skipper Sam Billings options.
Leg-spinner Nathan Sowter has performed admirably as the sole spinner since Rashid Khan left for international duty with Afghanistan last week.
Here he took 2-23 after Jamie Smith gave Spirit a fast start with 28 from 15, helping squeeze the scoring before 31 from 18 by Overton boosted the score.
Sowter may well be joined by Australia spinner Adam Zampa for the final, with Invincibles in talks with the 33-year-old over a one-game deal.
That would make their opponent’s task tougher still.
