Ayr United eased into the last 16 in a stormy tie which saw Arbroath manager Dick Campbell sent to the stand after marching on to the pitch to confront referee Mike Roncone.
A double from Declan McDaid and goals from Lawrence Shankland and Craig Moore swept the Honest Men to victory, with sub Ryan McCord replying for the visitors.
The flashpoint came when Ayr’s David Ferguson seemed to haul down Danny Denholm but the referee waved played on.
Campbell said: “I haven’t seen a more blatant penalty in my life – if it’s not a penalty he has to book the player for diving. Every Ayr United supporter saw it.
“There is no word in the English dictionary to describe why it’s not a penalty.”
Ayr took an early lead when McDaid curled a shot into the top corner after a great crossfield pass by Shankland.
Arbroath started the second half on the front foot and they were almost level when Gavin Swankie turned on to a Bobby Linn cross and cracked a shot off the base of the post.
But Ayr put themselves in the driving seat with a stunning curling finish into the top corner from Shankland.
The tie boiled over when Arbroath seemed to be denied a clear penalty when Ferguson hauled down Denholm inside the box. An angry Campbell strode on to the pitch to confront referee Roncone, who immediately sent him to the stand.
Sub McCord pulled one back but McDaid wrapped it up after Shankland’s shot was parried.
Moore completed Arbroath’s misery in stoppage time and home boss Ian McCall claimed: “It could have been more. We cut them open and scored good goals.”