The problem with facing Antonio Conte’s Chelsea, as so many Premier League managers have discovered this season, is that their front three becomes a front five. In Monday night’s FA Cup tie at Stamford Bridge, José Mourinho responded by effectively deploying a back six.

Chelsea have overloaded the opposition frequently this season thanks to Eden Hazard and Pedro (or, in this case, Willian) drifting inside to positions close to Diego Costa, allowing Marcos Alonso and Victor Moses to push forward aggressively down the outside. Opponents are exposed when their back four is dragged to one side, leaving Alonso or Moses free at the far post, and the only response is for the opposition wingers to retreat, effectively forming a six-man defence.

Mourinho was perhaps the first manager to effectively accept the latter situation. Phil Jones and Matteo Darmian were fielded in nominal full-back positions, but instructed to man-mark Hazard and Willian respectively, often ending up in front of their centre-backs, Chris Smalling and Marcos Rojo. In turn, this forced Antonio Valencia and Ashley Young – two natural wingers who have often found themselves deployed at full-back over the past couple of seasons – to track back and cover the space on the outside of Manchester United’s centre-backs.

The approach was typically Mourinho, about being flexible and determinedly nullifying key opposition players, but also somewhat of a throwback to the Sir Alex Ferguson days. United’s approach in the full-back positions was somewhat reminiscent of the way Gary Neville and Denis Irwin tucked inside to track Youri Djorkaeff and Roberto Baggio during their famous 2-0 victory over Internazionale on the way to winning the 1999 European Cup, for example. Introducing Jones to man-mark the opposition’s key player was also something Ferguson did regularly during his final campaign when he pinpointed a dangerous opponent: Everton’s Marouane Fellaini and Tottenham’s Gareth Bale inflicted United’s first two defeats of 2012-13, and in the return meetings found Jones tracking them all over the pitch.

In the opening stages Mourinho’s unusual defensive approach, combined with Paul Pogba and Ander Herrera shutting down N’Golo Kanté and Nemanja Matic quickly in midfield, caused Chelsea real problems. Chelsea’s back three struggled to find a positive forward pass, with every other player tracked comfortably. United’s pressing was impressive, they circulated the ball effectively, and played the majority of the first 15 minutes inside Chelsea’s half.

Conte’s side adapted impressively, however. Hazard and Willian realised they were under close scrutiny and started to vary their positions more dramatically, with Hazard drifting into midfield and Willian moving across into an inside-left role. United were still attempting to man-mark, but Jones and Darmian clearly felt uncomfortable crossing to the opposite side of the pitch, and often let their opponents run free. Willian showed some lovely touches in possession, particularly with a couple of backheels into the path of team-mates which quickened the tempo, while Hazard became the game’s key player.

The Belgian’s drifts inside meant he was no longer simply watched by Jones, but also by Herrera – who was dismissed for two fouls on Hazard, the first a body-check, the second a trip when Hazard typically spun quickly after receiving possession. Although Hazard was not literally the matchwinner, with Kanté’s second-half long-range strike proving the game’s only goal, it was his movement which ensured Chelsea’s passing improved dramatically, and his trickery which resulted in Herrera’s dismissal, the contest’s turning point.

Mourinho immediately summoned Fellaini in place of Henrikh Mkhitaryan, which meant Marcus Rashford was now extremely isolated as United’s formation appeared 6-2-1 when Chelsea retained possession for long periods. Pogba, who had started brightly, was eventually overshadowed by Kanté, but this was simply a reflection of Chelsea’s overall dominance. With David Luiz able to step forward and dictate play, Chelsea were in control and Chelsea continually piled pressure upon United’s massed defence.

Rashford was forced to fend for himself up front, and turned a David Luiz mistake into a fine goalscoring opportunity which forced Thibaut Courtois to save smartly. But Mourinho made little attempt to change things significantly – Jesse Lingard on for Young was his only second-half substitution, and former Chelsea playmaker Juan Mata did not get off the bench.

Mourinho may seek to replicate this plan for Chelsea’s trip to Old Trafford next month. One suspects, however, that Conte will have an alternative strategy of his own, and having increasingly used a 3-5-1-1 in the second half of matches recently, may start to use that system from the outset too.