Arsenal’s 2-0 victory at home to Bayern Munich a fortnight ago was built on the foundation of a solid defence, married to a relentless counter-attacking determination to prevail upon the German champions’ poor defensive transitions.

That Tuesday night, in the Emirates, the Gunners lined up in a defensive 4-5-1, preventing their much-vaunted opposition from playing through. Munich’s deep lying-playmaker, Xabi Alonso – sitting at the base of their 4-1-4-1 formation – was largely allowed to go free in possession owing to the way in which the two shapes matched up. Most of his side’s few chances stemmed from his weighted balls over the top of the Arsenal defence.

Bayern were forced wide by the compact nature of Arsenal’s defensive unit. Although Douglas Costa skinned his man, Hector Bellerin, on numerous occasions down the left, most of his crosses were repelled by the centre of the Arsenal defence – particularly by the excellent Per Mertesacker. As were the deep crosses of Philipp Lahm, emanating from the opposite flank.

Bayern were even more inept in the final third in the second-half, resorting to speculative attempted lobs over the head of left-back, Nacho Monreal, which the Spaniard dealt with comfortably.

Tonight, on the other hand, was a very different story – thanks in large part to a fascinating tactical innovation from manager, Pep Guardiola.

Guardiola made three broad changes to his side’s approach from the reverse fixture. Firstly, he changed the shape of his team. Bayern lined out tonight in a 4-2-3-1, with Thiago Alcantara joining Xabi Alonso in a double-pivot in front of the defence. Javi Martinez returned to the side at centre-back, with David Alaba restored to left-full.

Secondly, Guardiola changed the nature of his side’s wide threat. Two weeks ago, he opted for Douglas Costa on the left and Thomas Muller on the right – the former a genuine winger, the latter essentially a wide poacher. Here, he instead opted for two genuine wingers, with Costa starting on the right and the 19 year-old, Kingsley Coman, on the left.

The third change he effected was the aforementioned innovation. Although ostensibly fielded at left-back, Alaba regularly took up positions akin to those a number ten might occupy when his side approached the final third. Specifically, the Austrian looked to take up left-of-centre positions between the Arsenal lines. This posed a huge problem to Arsenal’s right-sided central midfielder, Santi Cazorla. The Spaniard was torn between picking Alaba up and pressing Bayern’s left-sided central midfielder, Thiago.

The effect of this dilemma was to leave Thiago free in possession more often than not. This freedom led to the opening goal after ten minutes, when Thiago availing of a complete lack of pressure to loft a beautifully weighted ball over the top of Arsenal’s defence for Robert Lewandowski to head home. Arsenal were also guilty here of their old sin of trying to play offside with no pressure on the ball.

Thiago completely dominated this game, completing 105 passes by its end. This was only seven more than the equally free Alonso, but almost 40 more than any other individual. He was also the game’s top tackler and chance creator, with Coman (in the first half), Robben and Muller (both late in the second) all wasting chances from Thiago through passes.

Not that Alaba was merely a decoy to facilitate the Brazilian midfielder’s dominance. The Austrian also put his side three goals to the good by picking up the ball in behind poor old Santi and unleashing a fantastic long-range drive past Petr Cech. The fourth also stemmed from Alaba moonlighting as a ten – drifting into the inside-left channel to pick up Costa’s pass and cutback for Arjen Robben to finish.

In addition to his Thiago/Alaba quandary, Cazorla was also faced with the reality of being unable to shuffle across and assist Arsenal’s right-side in dealing with Kingsley Coman – the focus of much of Bayern’s attacking play. This was another shrewd tactic from Guardiola, given Arsenal’s well-documented injury problems in that area of the pitch. With stand-in right-back Mathieu Debuchy sticking close to his centre-backs, stand-in right-winger Joel Campbell – he of one senior goal in four years – was completely overwhelmed.

The early opener was a huge blow for Arsenal as it forced them to open up and fall prey to the fast break. Bayern’s second stemmed from Philipp Lahm’s untracked overlapping run and cross. And, moments before the third, Bayern went close from a chance crafted from the same flank when Cech tipped over from Muller. Left-winger, Alexis Sanchez, and left-sided central midfielder, Mesut Ozil, were caught upfield.

In the second-half, Arsene Wenger instructed his side to open up even further, switching to a 4-4-1-1 shape, with Ozil in a right-of-centre, number ten role to give Alaba et al something to think about. Although they quickly went four down, Arsenal were the better side for large periods in this half. They successfully shut down Bayern’s left-sided threat, particularly when Alexis Sanchez was switched to that flank after Kieran Gibbs replaced Campbell. Sanchez completed six dribbles in the second-half, as opposed to one in the first and, along with Mesut Ozil, instigated several dangerous breaks that should have borne fruit for the visitors.

Cazorla should have scored with Arsenal’s second effort on target soon after Bayern’s fourth goal. Giroud’s acrobatic finish with twenty to go – created by Ozil and Sanchez – came as no surprise.

Although just a consolation, this goal prompted Guardiola to introduce Arturo Vidal in place of Lewandowski and revert to a 4-1-4-1 shape to close out the game. His side tacked on a fifth in the last minute of normal time from a fast break when Costa played in Muller. In truth, it could easily have been six or seven, as Arsenal’s continued attacking abandon worsened their already-poor defensive transitions and led to several presentable counter-attacking chances that the Germans spurned.

This defeat, coupled with Olympiakos’ win at home to Zagreb, leaves Arsenal on the brink. Bayern march on. They will take some stopping. Particularly with a manager as shrewd as this one.