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A day usually celebrating their greatest competition turned into a farce for UEFA. 

Monday's last-16 draw for the Champions League was declared void after a 'technical error' in which teams went in to which pot. 

But how did it all unfold? Sportsmail's KIERAN GILL takes you through Monday's dramatic turn of events.  

The Champions League draw descended into chaos after Man United were drawn twice 

The Red Devils were eventually drawn against French giants Paris Saint-Germain for the last-16 but the English side will now face Atletico Madrid and PSG will take on Real Madrid

WHAT WAS MEANT TO HAPPEN? 

The draw to UEFA's grandest competition was supposed to go off without a hitch. 

Scheduled to start at 11am after their usual long-winded build-up, each tie for the Champions League's last-16 was to be drawn one by one. 

It starts with the group runners-up being drawn as the home team for the first leg. They are then paired with a group winner. 

But teams from the same group or country should be kept apart.

WHAT WENT WRONG?  

The first tie was straightforward as Benfica were drawn with Real Madrid. It went downhill from there, however. 

In the second tie, Villarreal were pulled out of the pot and then drawn with Manchester United, which was prohibited due to them both being from the same group. United's ball was set to one side and Manchester City were drawn instead. 

UEFA's Giorgio Marchetti intervened to say that United could not be drawn against Villarreal

In the third tie, Atletico Madrid were drawn with Bayern Munich. However, United were mistakenly omitted from the pot to face Atletico when they should have been included. 

Liverpool appeared to be placed in the pot instead when they should not have been, due to them being from the same group as Atletico.

WHO DID THE DRAW?  

Former Arsenal forward Andrey Arshavin was the unfortunate poster-boy of this big blunder. 

It wasn't his fault, however, as he was merely pulling out balls from a pot placed in front of him. 

Andrey Arshavin drew United out of a pot given to him by UEFA chief Michael Heselschwerdt 

Giorgio Marchetti, the UEFA deputy general secretary, was the man in charge of the ceremony and doing the talking, while Michael Heselschwerdt, the UEFA head of club competitions, was organising the balls from the various pots in front of him.

WHAT DID UEFA SAY?  

UEFA blamed it on a 'technical problem with the software of an external service provider that instructs the officials as to which teams are eligible to play each other'. 

Their officials were blindly following this system, with Heselschwerdt using it to know which balls to pick from the different pots. 

United were also accidentally omitted from the pot to face Diego Simeone's Atletico Madrid

United had already played Spanish side Villarreal in the group stage so couldn't meet again 

WHAT HAPPENED NEXT?  

Social media erupted during the cock-up, with calls for a new draw because of the controversy. BT Sport kept their pundits - Joe Cole, Michael Owen and Owen Hargeaves - at the studio in case it needed to be redone. 

The chances of a redraw increased as several clubs contacted UEFA to complain, claiming this tainted the competition. Real Madrid wanted their original tie to stand, however. 

They were handed a favourable tie with Benfica before the blunder took place and it is understood they felt their match should therefore have remained untouched.

Instead, the decision to re-run the draw in its entirety left them with a two-legged tie against Paris Saint-Germain.