The home side were quickly on to the front foot, former Don Max Barry very prominent as they pushed forward, but Aberdeen defended well and Tom Ritchie's goal was never under serious threat although it took a fine Mykyta tackle to thwart Urquhart.
Duncan and Virtanen combined well on the right as the Dons grew into the match but Ruth's header from Duncan's cross was easily gathered by Main.
The Dons came close on 16 minutes but Barron's free-kick slid the wrong side of the post. Mykyta was looking good spraying passes from the middle of the park and he tested Main from distance, but again the keeper's handling was excellent.
It was looking like either only an error or an unexpected flash of brilliance was going to produce a goal as both sides threatened to cancel each other out. Sadly for the Dons it was the latter.
A long clearance came off an Aberdeen head and fell short of Ritchie allowing the alert Scott Adams to nip in and lob the ball over the helpless keeper and into the net.
Just before the break the same player almost made it two, his shot drifting wide after more good work from Barry.
Half time - Buckie Thistle 1 Aberdeen 0
During the interval Evan Towler replaced Kieran Ngwenya, who also featured for the first team in midweek. Early in the half the Dons tried to impose themselves on the game with Connor Barron doing his utmost to get his team driving forward.
Midway through the second period the Dons thought they had drawn level. A Mykyta free-kick was flicked on by Ruth and Kevin Hanratty lashed the ball into the roof of the net only to find the linesman had flagged him offside.
That near thing spurred the home side on and a dazzling run from Sam Urquhart deserved better than a MacAskill header slipping past the post. Buckie were proving very resolute in defence and clear cut openings were hard to come by for the Dons.
Ryan Duncan's shot went straight down the throat of the keeper, but an equaliser just wouldn't come and Graeme Stewart's side managed the final stages brilliantly to earn themselves a crack at Formartine United in four days time.
Crowd ? 500
Referee - Lee Robertson. Assistants - Dave McLaren and Will Adam.
"For this group, it was their first game. I think we looked nice on the eye up to a certain point and then we had no end product.
"We controlled the game in large spells but having 75/80% possession in games means nothing unless you score goals.
"We never looked our normal attacking threat and that can come down to fitness/sharpness and game time.
"We made a mistake and they capitalised on it.
2Every Aberdeen team no matter what age - we should be winning the game. That's the demands of the football club. But credit to Buckie, I thought they were outstanding. They defended deep, they worked hard and looked organised.
"Hopefully we can get some of the younger ones up to the first team squad but as you can see there's still a lot of work to be done. If you want to be a top player you need to stand out today and take the game by the scruff of the neck and our forward players especially didn't do that."