Slow left-armer Mfoza first claimed three for 23 in an outstanding four overs to help restrict the opposition to 110 for eight, before the in-form Erwee bashed 67 off 51 balls (7 fours, 3 sixes) as the Pietermaritzburg side coasted to victory with 32 balls remaining.
It was a third successive half-century for the opener after he recorded scores of 80 and 65 in KZNI’s previous two games.
But the hard yards at the Diamond Oval had already been put in during the first half of the contest by the bowlers in his side.
After winning the toss and bowling, they had complete control over Gauteng from the outset.
Key duo Ryan Rickelton (3) and Mangaliso Mosehle (0) were out inside the first two overs when they fell to Gareth Dukes (1/22) and Kerwin Mungroo (1/6) respectively.
Yassar Cook (24) helped stabalise things for a while, before he fell to Athi Maposa (1/19).
It was then down to 20-year-old Mfoza, who was playing in just his third match, and he cut through the middle order, including taking the wicket of top-scorer Shaylen Pillay (25), to ensure Gauteng set just 111 for victory.
The Johannesburg side needed something special to stop KZNI, but after getting the wicket of skipper Lefa Mosena (7) cheaply, they could not stop the flying Erwee as he took the game away from them with a thrilling knock.
Support came through Grant Roelofsen (20) and Kyle Nipper (15 not out) as the 2015 runners-up reached the final for the second time.