Potton won the toss on Friday night and put Park into bat.
Southill made 154-9 off their 15 eight ball overs, their top scorer being Ajay Momi (52 off 44 balls), with support from Lee Hoggett (22), until both were run out.
However Southill regrouped with two quick fire contributions from Hani Thiarri (36 off 19 balls) and Jack Good (27 off 17 balls).
In reply Potton just about kept pace with the required run rate for a while, but once Ben Welch was out for 34 after nine overs, the innings tailed off.
Potton were finally all out for 107 off 14.2 overs.
Dominic Chatfield took four wickets for 27 off his four overs, and Good 2-29 off his four while Momi snapped up three catches in the field.
Good’s performance with bat and bowl earned him the Man of the Match award from the two umpires, Geoff May and Matthew Stevens.
Competition records show that Southill Park had previously won the Heritage Cup just once, back in 1991 and it was fitting that two members of that winning side, Graeme Lamb and John Wisson were present to support the team at the The Hollow.