Pep Guardiola has used a back three on three occasions this season, but he has not had the best players to carry it out effectively until now.
The first occasion, against Everton on New Year's Day, saw Fernandinho, Eric Garcia and Rodri play at the back, with Aymeric Laporte and Nicolas Otamendi joining Fernandinho in a back three at Sheffield United later that month.
Against Manchester United in the Carabao Cup semi-final second leg, Guardiola played right-backs Kyle Walker and Joao Cancelo either side of Otamendi, with Rodri and Ilkay Gundogan providing support from defensive midfield.
It's safe to say none of these back three combinations would be Guardiola's first-choice trio if he was to use the formation again as Manchester City prepare to restart their season.
With a fully fit squad to choose from ahead of the return of the Premier League, Guardiola might be tempted to explore the system again with a Champions League trophy in mind. A back three could give City more defensive stability in the last-16 second leg against Real Madrid, and hopefully going forward into the quarter finals.
Fernandinho's positioning with Aymeric Laporte and John Stones either side would arguably be City's best defensive trio, with Benjamin Mendy and Kyle Walker available as wing-backs to drop into a back five if needed or push on and provide width to the attack.
Then Guardiola has options with his midfield and attack, with one option being an offensive front three of Raheem Sterling, Sergio Aguero and Leroy Sane, with Kevin de Bruyne and either Rodri or Ilkay Gundogan alongside in midfield.
Alternatively, a more structured attack could incorporate the hard work and tactical discipline of Bernardo Silva, Gabriel Jesus and David Silva. Riyad Mahrez and Phil Foden are also capable of playing more tactical roles, depending on the situation City may find themselves in over a two-legged tie against one of Europe's best.
A back three, with the players at Guardiola's disposal, could also turn into a more familiar 4-3-3 if Fernandinho was to push forward, or it would only require one substitution to change system entirely.
Guardiola saw the value of a more disciplined formation and approach in the win at Real Madrid, but were let down by one lapse in defence that means Zinedine Zidane's side are in the tie. Now he might have the players to finally perfect a system with a back three that would provide the extra protection they need to progress in the competition.