Whitley Bay were within two minutes of causing a shock at Croft Park but eventually bowed out of the Northumberland Senior Cup as Blyth scored twice in the second period of extra time.
Spartans will now take on Morpeth Town who shocked Newcastle United U21s with a 3-1 away win in the other tie.
Alongside five players who made their debuts at the weekend, Bay manager Paddy Atkinson included another new signing from Gateshead, Andrew White, who took the place of the cup tied Dillon Morse.
The first chance of the game saw Blyth’s Michael Richardson firing over the bar when well placed.
But after just four minutes Whitley Bay stunned their higher ranked hosts, taking the lead when Robbie Bird seized on a weak headed back pass from Joel Dixon and slid the ball past peter Jeffries to silence the home support in the bumper crowd of close on 600.
Blyth quickly responded with Dan Maguire driving a shot over the bar as they went on to dominate proceedings, enjoying lengthy periods of possession, forcing Whitley to defend in depth for much of the first half.
But with keeper Sean McCafferty handling the ball confidently and Dominic McGarr commanding the centre of defence, Bay repelled all that Spartans could throw at them.
They could have doubled their lead after creating two chances shortly before the interval.
Both fell to Peter Watling, the first after the captain on the night battled past defender Alex Nicholson but saw his shot saved by Jeffries, and then Michael McMullen’s good run down the right ended with Watling dragging his shot narrowly past the upright.
The second half continued with Blyth in the ascendency and it took an excellent save from McCafferty to deny Dan Hawkins an equaliser just five minutes into the half.
After 69 minutes, Whitley came close to grabbing a second and potentially decisive goal after Kempster cut in from the left and squared the ball for Bird less than ten yards out, but Dixon did well to block his goalbound effort.
Two minutes later Phil Cave’s cross from the left was headed over the bar by Watling.
There were less than two minutes remaining of the 90 when Blyth finally pierced the Bay defence as Damen Mullen took advantage of a loose ball and drilled home a low shot from the edge of the area to level the score.
Spartans did their best to settle the tie in the five minutes of added time but Whitley held on and the game went into extra time.
The first period saw only one real chance for each side, Kempster bringing a save from Jeffries while at the other end a curling shot from Neal Hooks was superbly pushed over the bar by McCafferty.
Blyth finally went ahead in the fifth minute of the second period when a headed clearance out of defence by Blyth saw the ball played quickly to the other end where Maguire shrugged off the challenge from a tiring Bay defence and slotted the ball past McCafferty.
Substitute Paul King headed over from Jack Stanger’s cross as Whitley tried to rescue the game and force a replay, but less than two minutes from time another goal from Maguire confirmed Blyth’s place in the final.
There was still time for Bay’s Paul Chow, who came off the bench at the start of extra time, to go close, but under pressure from Jeffries he put a cross from Hylton Laws just the wrong side of the post.
A battling and encouraging display from a ‘new look’ Bay side who pushed the in-form Spartans all the way, and despite their defeat they deservedly received a rousing reception as they left the pitch.
Whitley Bay: McCafferty, McFarlane, Cave, Stanger, McGarr, White, McMullen (Chow 90), Williamson, Watling (H Laws 111), Bird (King 82), Kempster.
Subs not used: McDonald, Gladstone.