Josh Bailey's first half red card gave MK Dons a mountain to climb, but they were already two goals down by the time he walked for a lunge on Leeds winger Keenan Carole.
It was always going to be a tough assignment for the EFL Alliance side, up against Premier League 2 Division 2 opposition, and once they went a man down they struggled to contain Leeds' attackers, who found space on the outside to repeatedly cause problems and create chances. Joe Snowdon scored the opener, Morten Spencer grabbed the second and then with the visitors down to 10, Leeds took full control. Max McMillan grabbed the third and although MK Dons hit back through James Holmes, it was 4-1 by half-time, Cian Coleman finishing well to quell any hopes of an unlikely comeback.
In the second half Snowdon and McMillan both got their second goal, before late strikes by Billy Fewster and Jimiel Chikukwa, on as substitutes for Spencer and Alfie Hughes respectively, completed the rout.
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Tali Jallow's 90th minute goal was barely a consolation for MK Dons, as 8-2 winners Leeds eased into the next round where they will face Newcastle United.
The Whites streamed the goalfest live on their Twitter account, allowing Thorp Arch graduate and first team star Kalvin Phillips to tune in, along with former striker and fan favourite Luciano Becchio and a number of the club's current Under 23s players.
Leeds United: Christy, Sutcliffe, Kachosa, Coleman (Rigby 80’), Teale, Leverett, Hughes (Chikukwa 69’), Spencer (Fewster 50’), McMillan, Snowdon, Carole. Not used: Brook, Pilkington, Bradbury, Littlewood.