The Scottish Championship favourites swept aside the Highland league champions in the Betfred Cup at Victoria Park.
Goals from McMullan, King and Durnan were enough for Dundee United to take the three points, leaving them in a nice position to get out of the group.
This was the second defeat for the Jags in the tournament and they travel to Dens Park to face Dundee on Saturday in the hope of keeping their slim cup hopes alive.
The first chance fell to ex Celtic midfielder Paul McMullan when his effort from inside the area was saved superbly by Daniel Bell to prevent the Tangerines from taking the lead.
The experienced James Keatings fired a free kick from 25 yards out narrowly over the bar minutes after the McMullan chance.
The deadlock was broken 17 minutes in after a mix up with Lewis Mackinnon and John Maitland meant the cross couldn’t be cleared and McMullan volleyed home 8 yards out.
Hibs loanee Sam Stanton then teed up ex-Hearts winger Billy King, and from outside the area he rifled an effort low beyond Bell to double the Dundee side’s lead.
Buckie’s first chance fell midway through the half but McLeod couldn’t generate enough power on his header from a Chris Angus thow in.
The Highland League champions were unlucky as some neat one-two passes allowed Copeland to send Angus through on goal, but Lewis was quick off his line to prevent the forward from cutting the deficit.
With 10 minutes to go before the break centre half Mark Durnan rose highest in the Buckie area to head a third from Keatings' corner.
Minutes after the third another Keatings corner caused a whole lot of trouble as captain William Edjenguele headed an effort goalward, however it was cleared off the line by Andrew Skinner.
Somehow United never added to their lead when McMullan put it on a plate for King at the back post, but the winger couldn’t get a connection on the ball.
Bell was then quick off his line to deny Congolese striker Patrick N’Koyi, who was through one on one with the keeper.
Buckie’s best chance of the half fell just minutes before the break, but Mcleod couldn’t beat the Southampton loanee Harry Lewis.
The Highland League side kept it tight in the second half and prevented United creating very much, with Bell saving the only clear cut chance of the half from Stanton.
There was a worrying moment for Tangerine’s boss Ray McKinnon as forward James Keatings had to be stretchered off the park after a challenge with a Buckie defender, which reduced the Terrors to 10 men.
Captain Fraser had an audacious effort in the dying minutes but he couldn't trouble Lewis in the visitor's goal.
Buckie fought hard but the class of the full time opposition was clear to see and they ran out comfortable winners in the end.