Paddy Parke's Seamer side had to battle back from 2-0 down at Eskvale & Cleveland League side Lealholm.
The villagers raced into a 2-0 lead after only 10 minutes due to a couple of defensive errors by Seamer, and the score remained this way until the half-time interval.
Ten minutes into the second half a rejuvenated Seamer pulled a goal back through Chris Stubbings, and five minutes later a cracking 30-yard free-kick from right-back Luke Purvis brought the scores level.
Left-back Ben Mason toe-poked the ball home to put Seamer in front and the final spot was confirmed when Gaz Lawton converted a chance soon afterwards.
Seamer then missed several chances to add to their lead and were almost made to pay when Lealholm were awarded an 85th-minute spot-kick, but the hosts missed and their chance to stage a late revival had passed.
Parke said: "The lads all played well in the second half but our man of the match was Purvis, with Jamie Hartley also doing very well for us."
West Pier had a much more comfortable time in their semi-final, sweeping aside York League side Kirkby 4-0.
Pier took the lead with an excellent early strike from the in-form Martin Cooper, but despite dominating the opening 45 minutes the Scarborough League Division One title-chasers were only 1-0 up at the interval.
The hosts scored their second shortly after the break through Billy Logan and then made the game safe on 70 minutes when the evergreen Paul Provins finished off a great team move. Sam Garnett's late tap-in completed the scoring.
Boss Andy Spivey said: "We were sound at back with Steve Sheader, Mikey Pickering, Andy Sheader and Jim Wardle stifling Kirkby's rare attacks. "Provins and Logan were lively up front, supported well by Tommy Barker and Cooper with Will Jenkinson and Garnett bossing the midfield."
Newlands Park eased into the Coastal Shellfish League Cup final with a 7-0 win at Filey Town Reserves.
Ben Luntley, Sean Exley and Matt Griffiths netted two goals apiece for the top-flight side, with Dan Freer also on target.
Park boss Shaun Mancrief said: "Filey started very well but fitness told in the end on a terrible pitch. Griffiths and Brad Rowley shared our man of the match award."
Itis Itis Rovers romped to an 8-1 win at home to Goal Sports to earn their place in the Frank White Trophy final.
Luke Jones banged in a hat-trick for the hosts, who led 5-0 after 30 minutes. Ali Jones, Ellis Wilson, Dave Young, Ryan Megginson and Sam Pickard, from the penalty spot, also notched for Rovers.
Paul Hill hit the consolation for Mark Plumpton's side.
Luke Jones and Curtis Rose were named as the joint men of the match for the triumphant hosts.