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Oldham boss Mellon appeared to thrust his head towards the Sheffield Wednesday man, who hit the deck as tempers boiled over at Boundary Park.
The flashpoint triggered an furious melee, with players and coaching staff from both sides piling in as the confrontation threatened to spiral out of control.
Mellon was eventually shown a red card and ordered to the stands following the extraordinary scenes.
And the footage does the 54-year-old few favours, with the former Dundee United and St Mirren manager now potentially facing further punishment from the FA.
There was more than a hint of irony surrounding Mellon's early exit, too.
The experienced boss had spoken warmly about his love for the famous competition ahead of kick-off and the special moments it has produced throughout his career.
Oldham Athletic manager Micky Mellon is shown a red card for moving his head towards Wednesday's Callum Slattery 🟥 📺 Stream on TNT Sports & HBO Max: https://t.co/fRCRh6tXYB https://t.co/5QMxgLt0dO
— Football on TNT Sports (@footballontnt) November 8, 2026
But Mellon's latest FA Cup memory could prove one he would rather forget after becoming the central figure in a remarkable touchline bust-up.