Wigan's win over Manchester City was an amazing game to witness and it has to go down as one of the greatest FA Cup shocks of all time.
When the Latics beat City in the 2013 final it was a big enough upset, but that was when they were a top-flight club, not in League One as they are now.
Then you consider the level Pep Guardiola's side have been performing at all season, how far clear they are at the top of the Premier League, and that they were trying to do the Quadruple.
It was mentioned to me before the game that Wigan could look at what Rochdale did when they held Tottenham on Sunday and be inspired by that, which is true.
But once I saw names such as David Silva, Sergio Aguero and Leroy Sane in the City line-up, I honestly did not give Paul Cook's side a chance.
With attacking power like that in City's side, I did not see how Wigan could contain them. However, helped by a special atmosphere at the DW Stadium, they defended brilliantly and took their chance when they got one.
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Red card splits opinion - but why yellow first?
Wigan boss Cook said afterwards that everything had to go in his side's favour for them to get a result, and that was the case when City were reduced to 10 men before half-time.
Fabian Delph did go in a bit recklessly on Max Power and he was slightly out of control, but I think he was unlucky to be sent off.
It is not as if Delph went in studs high and really tried to hit Power - it looked like he just over-stretched for the ball.
I thought a booking was the right decision but the poll on the BBC Sport website, where 69% thought it was a red card offence, showed it split opinion even when people saw it more than once.
That shows it was a 50-50 call, but the controversy over the decision came because referee Anthony Taylor appeared to get a yellow card out first and write Delph's name down, then subsequently pull out a red.
Taylor might have been influenced by the Wigan players who surrounded him, but I think it is more likely he had some sort of communication with his assistant too.
Whatever happened, we would not still be talking about it if he did not get a different card out first.
What made Grigg goal a special finish?
The red card did not change the pattern of play, because even with 10 men City still dominated possession and controlled the game - in fact, Wigan probably had more opportunities in the first half.
After half-time, the home side looked nervy. They were defending very deep and had to make a lot of clearances without being able to put their foot on the ball because they were under so much pressure.
With the Latics struggling to string four or five passes together and find any real momentum, Will Grigg did not get any chances, or much support, and he was really isolated up front.
The one chance Grigg did get in the second half, though, he took brilliantly.
It was impressive how quickly he anticipated the situation when Kyle Walker allowed the ball to run under his feet, and also that he recognised the England right-back would have the pace to recover.
So he stepped across the City defender and although he lost his footing as he opened up his body up to shoot, he was still able to steer the ball past Claudio Bravo.
It was Wigan's only shot on target in the entire game, but it was a great finish. That is what you need to do to get a result against the top teams - hold out valiantly, then take your chance when it comes.
Will defeat knock City out of their stride?
It turned into a brilliant night for Wigan and they have now beaten three Premier League teams to reach the quarter-finals - Bournemouth, West Ham and City.
It has been an amazing run for them already and next up they host another top-flight side, Southampton, with both teams aware Wembley is only one game away.
The worry for the Latics is that the FA Cup is a distraction from their bid to win promotion from League One, because their league form has dipped in recent weeks.
It is great they have got on this run again but I know promotion is their priority this season - Cook was quick to stress that when he spoke to BBC Radio 5 live after the match - and they need to get back on track.
As for City, they have a huge game on Sunday with the EFL Cup final against Arsenal, but I don't see this defeat knocking them out of their stride.
They responded to their defeat by Liverpool in January by winning four straight games and they certainly did not change their style of play.
All this defeat does is lead us all to wonder how they will react, and whether they have got the calibre of players to cope.
The Quadruple is gone now, but they can still win the treble, and I am expecting to see a very strong response from them this weekend.
Kevin Kilbane was speaking to BBC Sport's Chris Bevan