Phil Smith's verdict: The big dilemmas Lee Johnson will have to weigh up after Sunderland's battling cup win
If there is an easy win to sum up this often difficult but ultimately uplifting cup win, it's that it is now very difficult to second guess who will get the nod when Lee Johnson selects his XI for the return fixture on Saturday afternoon.
To a certain extent, this 3-0 victory showed that we can perhaps become too fixated on the starting XI, especially in this COVID-19 era. .
When the EFL confirmed earlier this season that clubs would be able to make five substitutions within games, the reaction at Sunderland was overwhelmingly positive.
The club had enthusiastically supported the move, hopeful that their squad depth would make it a point of difference in tight games against League One rivals.
It never quite worked out that way initially.
Partially because of a habit of making substitutions towards the end of games, but also due to a lack of real variety in forward areas.
It was telling then, that Lee Johnson pointed to his quadruple substitution on the hour mark here as a potentially important moment.
It was a 'brave' move, but one that underlined the importance of rotation in the hectic schedule ahead.
At that stage, Sunderland were beginning to lose their way in this game.
MK Dons may sit in the lower reaches of League One as it stands but no one who saw the way they outplayed, outpassed and outran the Black Cats at the Stadium of Light earlier this season would have taken this win for granted.
In the opening half an hour, they had dominated possession without causing too much damage.
Crucially, Sunderland had retained a threat of their own.
It is true that they had taken a 1-0 lead into the interval without a single shot on target, but it wouldn't be entirely right to say this meant they had not caused their opponents any issues.
Happy to cede possession the visitors may have been, but they always left at least three players in advanced areas and their pressing was aggressive.
On a number of occasions they broke into threatening areas, only the final ball preventing them from turning it into a meaningful attempt on goal.
MK Dons, though, became increasingly threatening either side of the interval.
Scott Fraser was a player Sunderland were keen on before the introduction of the salary cap, and he became the game's most influential figure as the host's extra man in midfield began to make a difference.
Fraser was picking up space at will and if not for some more composed finishing from Joe Mason, the Black Cats would have found themselves level at the very least.
So Johnson matched up his opposition, and through a combination of the extra security off the ball and the fresh legs on it, helped his side restore some level of control.
There was a touch of fortune, too.
MK Dons created their best chance in the moments after the substitution, Remi Matthews making a superb stop down to his left just as it looked like Russell Martin's side would get the goal their play probably deserved.
There was little doubt, either, that Lee Nicholls should have done better with Aiden McGeady's low drive for the second goal.
This was a night when the narrow margins within the game went Sunderland's way.
There were performances all over the pitch that will have given Johnson pause for thought.
Significantly, this was Luke O'Nien's first start under the head coach and it is fair to say that the impression he made was overwhelmingly positive.
He began the game in central midfield and impressed, breaking up play effectively, pressing quickly and winning his individual duels.
An early injury to Callum McFadzean forced him into left-back and there his contribution was arguably even more impressive, one superb goal line clearance preventing Scott Fraser from scoring a certain equaliser.
With Jake Vokins likely to debut on Saturday after making a strong early impression in training, O'Nien has made his case for inclusion and he may well have done so in that central midfield position.
His replacement in midfield, Dan Neil, produced another mature performance that underlined his potential. There were one or two giveaways as he got up to the pace of the game but generally his poise and precision was a delight.
His first thought is always to move the ball forward and as Johnson tried to build a more expansive side, there is no doubt that this has made an impression on him.
After grinding it out with his team-mates through the early part of that second half, the youngster visibly grew in stature as his side began to threaten on the break late on.
In those forward areas there is much for Johnson to ponder.
Charlie Wyke will surely start on Saturday, his cameo off the bench here including not just another well-taken goal but some strong all-round centre forward play.
Who partners him is a tougher call.
Lynden Gooch brings so much energy to central areas when selected there, and in the early stages it was he more than anyone that forced errors in possession.
In the attacking midfield roles, McGeady was a constant threat and that bodes well as Jordan Jones builds his way towards full match fitness.
Jack Diamond's end product was erratic at times, but he started and finished the game very strongly and that drew a special mention from his head coach.
Consider, too, that Bailey Wright is expected to be available for selection and the decisions for Johnson to make are multiple.
This was another game which underlined that at this stage, executing Johnson's vision for 90 minutes is a challenge.
The fixture schedule means fatigue and it also means a lack of training time to implement ideas.
The positive for Johnson is that both at the start of games and within it, he is getting more and more options to find a way to win.