The system had stood largely as a two-and-a-half year Pompey ever-present.
Now Conor Chaplin has prompted a change – and the return to a Fratton Park 4-4-2.
I know everyone is into this 10 thing, I’m not – that is my own opinionJoe Gallen
Kenny Jackett’s desire to pair a centre-forward with the home-grown talent has prompted a twin strikeforce in the Blues’ past four matches.
Following injury to Brett Pitman, Oli Hawkins has instead been asked to partner Chaplin during life after the 4-2-3-1 system.
It signals the temporary end of the number 10 – a role Joe Gallen admits he is uncomfortable with.
And Pompey’s assistant boss believes the use of a conventional twin-pronged attack can reap more rewards than a striker operating in the hole.
Gallen said: ‘You could say we have played with two centre-forwards on the pitch a lot this season, with one in the number 10.
‘But I’m not really into this number 10 thing as much as others, I just see personnel and what that personnel brings.
‘If Conor Chaplin is supposedly playing that number 10, well Conor Chaplin is a centre-forward, so to me that’s another centre-forward.
‘But if you put a midfielder in there then it’s a bit different because that player’s natural way is he may get into the box, but he’ll be in midfield. So it’s probably not a 4-4-2.
‘Put the centre-forward in there and you could suggest it’s a 4-4-2 – and for the last few games we have kind of said “Just get up front with Oli”.
‘I think it’s a case of the big man and little man combo, just getting some sharpness around Oli.
‘The ball does go forward and Oli can hold it up, win a header or put in a strong-enough challenge so the ball just drops.
‘The thinking is you then have someone around there to pick the ball up and start playing.
‘It is the opportunity to put Oli and Conor up front and telling them to play close together.
‘Now there are two players up there and sometimes you can attack a bit better – and defend a bit better because you are attacking, it’s pretty basic stuff.
‘My opinion is a number 10 is a bit more defensive, but putting two up front makes it a bit more offensive.’
Hawkins, Chaplin, Pitman, Connor Ronan, Kal Naismith, Kyle Bennett and Gareth Evans have all been utilised in the number 10 role this season.
For Gallen, though, his preference lies with a second striker as part of a front two.
He added: ‘I know everyone is into this 10 thing, I’m not – that is my own opinion.
‘If that number 10 is a centre-forward then you put very offensive players in the wide areas and look as though you are playing four up front.
‘But that won’t work either because you’ll only have two in midfield.
‘I’m just not into this number 10 who does nothing until the ball comes to him, then does a little bit and does nothing again and doesn’t defend because that’s beneath him, and he doesn’t run in behind because that’s beneath him, too.
‘He is just this fancy dan who doesn’t really get you out of League One – I prefer a second striker.’