Was it a 4-2-3-1? Was it 4-2-4? Trent Alexander-Arnold suggested afterwards it was actually your old-fashioned 4-4-2.
Whatever, it wasn't the usual 4-4-3 and it was precisely what Liverpool needed to lift the mood following an unimpressive start to the season.
Jurgen Klopp knew something had to change, system-wise, after his team were repeatedly picked apart by Brighton in that helter-skelter 3-3 draw on Saturday.
Jurgen Klopp switched Liverpool's system from a 4-3-3 to more of a 4-2-3-1 or 4-2-4 and gained the rewards with a 2-0 win at Anfield
The German trusted his instincts, sacrificed a midfielder for an additional forward and saw his team dominate Rangers in a 2-0 Champions League win to get themselves back on track.