Worthing, four times winners of the Davies and Tate Trophy, will meet Littlehampton in what is sure to be a hotly contested semi-final on August 14.
In the other semi, East Sussex National take on Brighton and Hove. Both clubs have never been this far in the Sussex Inter-Club Matchplay Championship.
The matches will be played at neutral venues to be announced. The finals of the Trophy and Plate are scheduled for September 11.
The mood was upbeat at Brighton and Hove when team manager Phil Bonsall heard that ESN stand between them and a shock appearance in the final. He said: "That's perfect, it couldn't be better."
Worthing stared defeat in the face at Willingdon. The Trophy favourites came within an ace of going out until an amazing turnaround saved the day.
At one stage, Willingdon led 5.5-1.5 and only needed a single point from the remaining five singles to reach the semi-finals.
But Worthing's middle and lower order rallied to squeeze home by 6.5-5.5, leaving the host club shattered and convinced the visitors have the Indian sign on them.
This was the third meeting between the clubs in the last four years and a repeat of Worthing's 2003 victory.
In the early stages, it looked as though the foursomes could go either way but Willingdon lunched with a 2.5-1.5 advantage.
Manager Eric Reekie said: "Our order of play in the singles was crucial. A Chinese parliament was called for as they do in the SAS when backs are to the wall.
"I gave my views and asked for those of the team. We had to cover Willingdon's strength that would undoubtedly come at us from the front.
"I put young Craig Newman against Rob Hampson, Willingdon's big gun, followed by Scott Williams, Joe Doherty and Arwel Roberts. We needed to take two of those matches and then three of the back four."
But Willingdon's answer to Reekie's tactics was to sink their teeth deeper as Hampson beat Newman by two holes, Mark Hepburn overcame Scott Williams 2&1 and Rob Williams defeated Doherty by one hole. Now Worthing were 5.5-1.5 down and apparently on the way out.
But Worthing's strength in depth turned the match on its head as they took all of the last five games leaving Jack Hepburn, James Gietzen, Mark Wooten, Andy Theo and anchor man Charles Goodall astonishingly without a point between them.
The outstanding clash was Hampson against Newman which featured 14 birdies in total, eight to Hampson and six for Newman. The former Sussex champion left a memorable struggle with a rare smile although he had not provided Worthing with a hoped-for win.
Bognor had every reason to feel chirpy with a 3-1 foursomes lead and seven holes up on countback at Brighton and Hove.
This was a notable achievement as Bognor's best player, Ollie Turnill, was playing in the Brabazon Trophy.
Over lunch, the B&H team put their heads together with guru Bonsall and slowly the tide began to turn.
Steve Stark beat Simon Ostrom in the top singles and Gary Daw made it 3-3, defeating Darren Wright 3&2. This put the B&H level on countback.
Dominic Rainey holed a tricky 20-footer on the last green to halve with Tim Hoyles, the B&H team captain, and then Bognor inched ahead again thanks to victories by Steve Mitchell and Ollie Reddick. The seesaw had tipped 5-5-3.5 in Bognor's favour.
In mounting excitement and amid a flurry for restorers at the bar, the home supporters applauded Wayne Humprey and Alan Barnes accounting for Bognor's Dave Hicks and Andrew Brown by 3&2 and 5&4 respectively. This levelled the stakes with the B&H ahead on holes won.
Everything depended on the last match between Craig Millyard, who used to be an assistant at Ifield and reinstated two years ago, and Bognor's Andrew Field.
Crucially, Millyard holed a 25-foot putt at 14 to avoid going three down. Had his effort not disappeared from sight it would have been curtains. Inspired, he won 15 and 16 to draw level and the next was halved. The last hole calls for the tee shot to clear a high ridge and then dog-legs right. Millyard hit a beauty only for Field to end up in trees and thick rough.
Nevertheless, he produced an outstanding recovery to find the green while Millyard lay comfortably 15 feet away in two. Both two-putted for a half and that saw the B&H through 15-12 on countback.
Before a ball was struck in the Trophy this year, there was a quiet confidence at Littlehampton that they might go a long way. A series of home draws meant unhindered progress and Pyecombe were crushed 11.5-0.5. Seaford pushed hosts ESN hard at Little Horsted before bowing out 7-5.
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