There might have been a few fans scratching their heads when the team was announced at 2pm last Saturday.
Social media was certainly abuzz with theories on what system was being used and who would be playing where against Fleetwood.
When the game kicked-off, it became clear that Pompey were using a 3-4-2-1 formation, with Terry Devlin in an unfamiliar wing-back role.
A 1-0 win ensured it was a successful switch and John Mousinho is not averse to sticking with it.
The Blues boss said: "It's one of those things that players should be able to adjust to pretty quickly.
"Whether from being at other clubs or in academies, they should have experience of a number of different formations.
"I also think you should have that flexibility anyway – a centre-back that can play in a four should also be comfortable in a three.
"There aren't too many things that are dissimilar and we always work on different things in training.
"Having played with a back four for my first year here, I thought we did well at the weekend and I think it's something we can ask them to switch in and out of."
"It's one of those things that players should be able to adjust to pretty quickly."
Pompey are on the road again this weekend, visiting a Port Vale side who sit just four points above the League One drop zone.
Mousinho said: "If you remember the game at Fratton Park earlier in the season, they gave us a really tough 45 minutes.
"We had to adjust a couple of things at the break, although I thought we were the better side after that.
"But Port Vale have got a decent squad and they've been able to bring in some promising young players.
"They're well drilled and it's always a tough place to go, so we're expecting a decent contest on Saturday.
"It's tough to win games at this level – as we've seen from some of the results over the past few days."
Joe Morrell went off injured at Highbury Stadium, while Joe Rafferty missed the match completely with a neck problem.
Mousinho said: "Morrell is okay and we expect him to be fit for the game, but Raffs is a bit more touch and go.
"He's moving a bit better, although there is still some stiffness that will take some time to disappear.
"Ben Stevenson is probably still three or four weeks away after suffering some ligament damage in his knee."