Premier League quality shone through as a strong Southampton side ran out comfortable winners at stadiummk.
With a game on Saturday lunchtime, Karl Robinson made five changes for the clash with the Saints which included seeing Sergio Aguza and Cristian Benavente start.
A superb solo effort Jay Rodriguez handed Ronald Koeman’s men a fifth-minute, beating two men before curling home a fine finish off the post.
Cedric Soares and Oriol Romeu shot wide but Sadio Mane was clinical on 10 minutes to make it 2-0, pouncing on a loose ball before delicately lifting the ball over David Martin from a tight angle.
The Dons responded and, after receiving a clever ball from Diego Poyet, Carl Baker drove at the Saints defence before bringing a smart save out of Maarten Stekelenburg.
That signalled a decent spell for the men from MK1, however, they found themselves 3-0 down on 25 minutes when Shane Long broke the offside trap and teed up Mane, who cut inside and coolly slotted past Martin.
Northern Ireland midfielder Steve Davis burst through shortly afterwards but fired wide when well placed while, at the other end, Daniel Powell shot down the throat of Stekelenburg after cutting in from the right.
Juanmi headed over the top before the visitors were awarded a penalty after Antony Kay had fouled Rodriguez, who picked himself up to smash home from the spot on 49 minutes.
Virgil Van Dijk grazed the bar shortly afterwards with a dipping free-kick from 20 yards as the Premier League side’s quality continued to show.
Nicky Maynard came on for his debut just before the hour mark alongside former Saint Ben Reeves, who replaced Simon Church and Aguza respectively.
Southampton broke and made it 5-0 on 68 minutes, Juanmi racing down the right and delivering a dangerous cross which Kay attempted to clear but it hit Long and found the back of the net.
Substitution Rob Hall almost pulled one back with a curling effort from 25 yards, but the Dons fell further behind on 75 minutes when Long fired home a fine effort.
The men from MK1 were denied a late penalty when referee Keith Stroud waved away what looked like strong appeals for a foul on Maynard as he burst into the box.
There’s now a quick turnaround for the Dons, who will be looking to put things right on Saturday lunchtime when they host Derby County.
MK Dons: Martin; Hodson, McFadzean, Kay, Lewington (c); Aguza (Reeves 58), Poyet; Benavente (Hall 36), Baker, Powell; Church (Maynard 58).
Unused subs: Burns, Spence, Murphy, Rasulo.
Attendance: 10,189 (2556 Southampton fans).
Referee: Keith Stroud