Penzance won the Vitality Club T20 Area Finals at Port Talbot Town CC after two thrilling games.
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They dismissed Bradninch (Devon) in the second semi-final for just 70.
Ali Usman took 3-3 and Giles Lawrence 3-19 with two each for Christian Purchase and Tom Dinnis.
Remarkably Penzance then found themselves in danger of going out of the competition at 53-7 before squeezing home by one wicket.
Purchase was lbw to the first ball and Tom Wells and Antony Angove also failed to score.
Dan Lello made a vital 23 but it was Jonny Ludlam's nine off 19 balls that got them over the line.
He was caught at cover with two needed but the last pair of Glyn Furnival and Dinnis tied the scores with a wide and then a scrambled single saw Penzance through.
The first semi-final between the hosts, Port Talbot Town and Potterne from the West of England Premier League saw Port Talbot recover from 21-4 to post 134-6. Potterne won by six wickets with five balls to spare. Former Hayle batsman Graham Wiseman made 25.
Penzance elected to bat in the final and Purchase (15), Greg Smith (15) and Wells (14) all got starts. New overseas professional Ali Usman made 31 before being fourth out at 74. It was 99-7 with two overs to go but what proved a crucial 17 came off the penultimate over. Lawrence hit successive boundaries, sandwiched by four byes. Ludlam then hit a boundary before being stumped. Lawrence and Dinnis only managed four off the last over but the 120-9 ended up being more than looked possible at one stage.
In a remarkable start to the Potterne innings Basil Akram hit Lawrence for a six, second ball, before being stumped off the next by Rhys Brownfield and Wiseman was caught off the last ball of the over by Jack Paull. In a tight spell the left arm spin of Ali Usman reduced Potterne to 46-5 in the ninth over. The Wiltshire side were kept in the game thanks to a seventh wicket stand of 50 from Joshua De Souza (24) and Jake Goodwin (37). However, the rate had risen to 25 required off the last two overs. Ludlam struck a vital blow to remove Goodwin. With 22 needed off the final over Wells was introduced and picked up the last three wickets for eight runs to leave Potterne 14 runs short of victory on 107 all out.
Penzance now progress as one of four teams to the Southern Regional Finals day at Basingstoke & North Hants on Sunday 15 August.
(1) Alton (Southern PL) or Tunbridge Wells (Kent PL) (August 8) v Slough (Home Counties PL)
(2) Penzance (Cornwall PL) v Brentwood (Essex PL)
The four Northern winners will similarly compete at Danby CC in Derbyshire:
Alderley Edge, Appleby Frodingham, Barnard Castle, Westhoughton.
The two Regional winners will contest the National Final at a First Class ground in September.
The competition has been running since 2008 when St Just reached the National Finals Day and repeated it in 2011.
Vitality Club T20 Competition (Cornwall) homepage