With the likes of Mesut Ozil, Marco Reus, Tomas Rosicky, Henrikh Mkhitaryan and Jack Wilshere all featuring, few probably expected the winning goal in Borussia Dortmund's defeat of Arsenal to come via Kevin Grosskreut, a hard-working but technically limited utility, but so it proved decisive. It was particularly appropriate in the context of the tactical battle, given the battle between two compact 4-2-3-1's and surprisingly high lines, which congested the centre of the pitch and funnelled attacks out wide.
Aside from an initial period of heavy pressing from the home side, the relatively slow nature of proceedings also helped, with both defences instigating moves slowly from deep and thus encouraging their full-backs to get forward. Nuri Sahin dropped in between Mats Hummels and Nevan Subotic, making it enormously difficult for Olivier Giroud to cover the distance across Dortmund's defensive line -- especially with Ozil barely contributing defensively -- and so the three deepest Dortmund players had the freedom and space to instigate passing moves.
Compare that with the bustling energy of Dortmund's band of three, who showed a willingness to close Arsenal's back four down furiously in the opening ten minutes before settling into a more reserved nature -- but importantly, still working hard to shut down forward passing angles.
Still, Arsenal managed to work the ball into dangerous positions in the wide areas. Bacary Sagna whipped in a fine ball for Giroud to score the equaliser while Kieran Gibbs too overlapped manfully down the left, flourishing particularly when Santi Cazorla came on to balance out Arsenal's trio of fleet-footed playmakers. Having featured in that hybrid left wing / playmaker position prominently throughout 2013, Cazorla timed his drifts inside more fluently than Rosicky, who seemed unsure of his role both in and out of possession.
However that clarity of understanding and the more cohesive Arsenal attacks that followed turned to be their downfall. As Gibbs creeped forward more and more the space he was vacating in behind became more and more obvious and despite previous wastefulness, Grosskeutz managed to find Robert Lewandowski waiting inside the penalty area for the winning goal.
Arsenal had not been punished but they had certainly been warned, with Grosskeutz having earlier slipped in behind Arsenal's back four but the quality of his final ball woefully underwhelming. It illustrated the home side's naivety. At 1-1 it was risky to allow Gibbs and Sagna to continue driving forward, especially with the obvious threat of Dortmund's lighting counter-attacks, and so it proved decisive in an otherwise tight encounter.