Hornets were unlucky to lose by such a margin as they played the better passing football in this cup tie, but the East Lothian outfit showed the home side the way to goal with a much more direct route.
Dunbar coach, David Souness, said: "The scoreline flattered us but it was a cup tie and the result was very welcome."
The home side had moments early in the game when they could have hit the back of the Dunbar net, but their shots at goal were too often wide of the target or too close to goalkeeper Chris Backie, who impressed.
Ross McLeod went close to getting an opener for Vale, but his volley went wide of the post. While Hornets mounted good attacks playing their tidy passing football, the visitors sent long balls over the home defenders into space and that allowed the quick Dunbar forwards the chance to make tracks towards Phil Talbot in the Hornets goal.
The home side gave away several free-kicks and that allowed big central defender Kari Main the chance to use his height and considerable physical presence in the Vale goalmouth.
But it was Dunbar skipper, Kieran Simants, who notched the first goal of the game, running in to head the ball over Talbot following a great free-kick from Main.
Talbot then produced two great saves to deny Dunbar another goal and when play surged to the other end, Ross Cain ran in from the left to send a well-hit shot towards a gap at the near post but Backie threw himself across goal to deflect the ball for a corner.
Vale continued to attack the visitors' goal but the big Dunbar defenders held out.
In another Vale attack, they got the goal their play deserved and it was Scott Begbie who was perfectly placed in front of the Dunbar goal when a ball broke to him and the Vale No.6 sent a low shot past the unsighted keeper to make it 1-1 at the half-way stage of this refreshing and honest game of youth club football.
With Vale pushing forward for a second goal on the restart, they were caught out when a great clearance sailed over their defence and Liam Venables ran with the ball from near the half-way line to send a wonderful shot over the advancing Talbot and the ball crashed into the net just under the crossbar.
The East Lothian side never looked like losing the game after that great goal. In another attack on the home goal, the Hornets defence did not clear the ball and Simants fired a low shot into the net from an acute angle to put Dunbar further ahead at 3-1.
Dunbar's greater physical strength allowed them to take command in midfield but a nice passing move involving several Vale players created a half-chance, but the final shot was disappointing and the ball flew wide.
Main used his strength again to rob Sampson of the ball in a midfield joust then sent a searching pass up the left. That gave Ross McKenzie the chance to use his pace to outrun his marker but he spoiled it by firing the ball wide of the Vale goal. The tiring home side lost the ball again in midfield and Venables was off again, but the Vale defence got back in time.
In the closing stages Dunbar dominated proceedings and they went on to clinch their place in the second round of this prestigious local cup event with further goals from Jack Fairbairn and Ryan McGovern. It was a cruel result for Hutchison Vale Hornets as they put so much in to the game.
A Vale parent said: "Hornets played good football but they were not able to penetrate the Dunbar defence. The final pass let them down time after time."
Hutchison Vale Hornets: Phil Talbot, Ross Cain, Mathew Sampson, Scott Smith, Stewart Wilson, Jed Haston, Ross McLeod, Calum Wylie, Craig Robertson, Scott Begbie, Stuart Sinclair, Mathew Cronin, Joshua Low, Paul Sheerin, Ben Cooke.
Dunbar: Christopher Baikie, Jack Fairbairn, Ben Campbell, Alexander Northcott, Kari Main, Scott Souness, Kieran Simants, Dominic Mayo, Ryan McGovern, Ross McKenzie, Antoin Penrose, Liam Venables, Jack Massie.
Referee: Chris McGregor.