Robert Lewandowski’s late goal gave Dortmund an important victory at the Emirates.

Arsene Wenger was without the concussed Mathieu Flamini, so Aaron Ramsey returned. Santi Cazorla isn’t yet at 100% fitness, so Tomas Rosicky replaced him on the left.

Jurgen Klopp is still without Ilkay Gundogan and Lukasz Piszczek, while on the right, Jakub Blaszczykowski started rather than Pierre-Emerick Aubameyang.

This was a relatively tight, evenly-matched game almost entirely based around the positioning of the full-backs: Arsenal’s Bacary Sagna and Kieran Gibbs, and Dortmund’s Kevin Grosskreutz and Marcel Schmelzer.

The key issue #1: high lines

Both sides started with high defensive lines, which compacted the play into a thin strip either side of the halfway line. This meant that the full-backs found themselves in advanced positions extremely easily – it only took a 30-yard run, and they found themselves breaking in behind the opposition defence.

In this respect, the game was similar to Dortmund’s 2-1 defeat at Schalke last season, another match where the forward runs of all four full-backs was a key feature.

The key issue #2: relatively slow tempo

The game was played at a faster pace than many other Champions League games, certainly, but this wasn’t the ultra-energetic Dortmund that started last season’s semi-finals and final with astonishing pressing high up the pitch.

Although they closed down rapidly during the first 5 minutes, and their ‘gegenpressing’ resulted in the opener when Ramsey was caught on the ball in a dangerous position, for long periods the midfielders were able to put their foot on the ball and passing moves flowed at a gentle pace from defence to attack. Therefore, the full-backs had time to motor forward and stretch the play – less possible when a side is attacking directly.

The key issue #3: Arsenal’s midfield narrowness

Wenger is still without his three first-choice direct options in wide positions: Theo Walcott, Lukas Podolski and Alex Oxlade-Chamberlain. Therefore, he’s playing ball-players rather than proper wingers in the wide roles, and both Jack Wilshere and Rosicky moved inside into the centre of the pitch.

In response, Dortmund’s players also moved very narrow with the ball – leaving the flanks bare for the full-backs to storm into.

The key issue #4: Dortmund shift shape

Against Napoli, it was particularly obvious that Klopp wanted to drop a central midfielder into the back and push the full-backs on, turning Dortmund into something like a 3-3-1-3. The insistence on changing formation cost them the game.

That happened a couple of times in the opening stages, and although the formation change wasn’t a regular occurrence, it was common to see one of the two central midfielders in a deep position, not looking to get forward, when both full-backs were in advanced positions.

UEFA.com’s average position diagram from the first half demonstrates the space the full-backs had to break into – particularly the Dortmund duo.

In all, the full-backs had the perfect environment to get forward, and there were several examples of their contribution.

The result: constant crossing opportunities for the full-backs

4 mins: Dortmund counter-attack and Gorsskreutz gets space in behind Rosicky – he shoots wastefully over the bar, rather than crossing.

9 mins: Marco Reus is on the right flank and tries to feed Grosskreutz – Rosicky is tracking him, and the pass is intercepted, but the right-back is briefly Dortmund’s most advanced player.

11 mins: Rosicky moves into the centre and plays a crossfield pass for Sagna, in plenty of space. He surprisingly decides to cut inside onto his left foot, then plays a poor pass intended for Ramsey’s overlapping run.

11 mins: Rosicky is in a central, narrow position trying to press Dortmund’s midfielders – Grosskreutz receives the ball in behind him, in 20 yards of space. Dortmund play a 3 v 2 into the box.

15 mins: Schmelzer gets space in behind Mesut Ozil, who is briefly covering Wilshere’s position, drawing Sagna out of position to close him down. He passes inside to Reus – whose pass goes astray, but he immediately wins the ball back on the edge of the Arsenal area, and Henrikh Mkhitaryan scores.

21 mins: Rosicky is again narrow, while Olivier Giroud is occupying Grorsskreutz. Gibbs has space to attack into, but his first time cross is overhit.

26 mins: Rosicky is yet again narrow, Ozil isn’t quite covering for him, and Grosskreutz again has the run of the flank. His first cross is poor, but he remains in space on the overlap, getting a second chance to cross, which causes brief panic in the Arsenal defence.

29 mins: Wilshere is off the pitch, so Schmelzer has space to advance into, sending in a dangerous cross with four Dortmund players in the box – it’s cleared by Mikel Arteta.

33 mins: Wilshere and Ozil combine down the right, bringing Dortmund’s left side out of position. Sagna charges forward, with Giroud waiting in the middle – but the right-back’s cross is straight at Roman Weidenfeller.

41 mins: Sagna brings the ball over the halfway line, plays the ball to Ramsey and continues his run into space. Schmelzer isn’t close enough to tackle, so Sagna stops the ball almost dead, steadies himself and whips in a near-post cross – Weidenfeller and Mats Hummels get in each other’s way, and Giroud scores into an empty net.

45 mins: Mkhitaryan brings the ball forward, looks right and finds Grosskreutz in acres of space with Rosicky nowhere to be seen – the right-back ends the first half how he started it, blazing over from long-range.

47 mins: Lewandowski receives the ball with his back to goal, looks up and finds Grosskreutz in space yet again – Gibbs has to sprint over and make a sliding tackle inside the box.

50 mins: Neven Subotic hits a long diagonal towards Grosskreutz – Gibbs intercepts with a header, but again Grosskreutz is the most advanced Dortmund player.

56 mins: Dortmund attack down the left, then quickly switch the ball to the right. Grosskreutz is all alone, breaking past Wilshere, with a tremendous opportunity to deliver a good ball from inside the box – but his weak cross-shot is straight at Wojciech Szczesny.

63 mins: Arteta switches the ball right, then left, where Gibbs has space – his forward pass to substitute Santi Cazorla forces a smart invention by Weidenfeller, at his near post.

70 mins: Grosskreutz collects the ball in space and launches a deep, lofted cross towards Lewandowski. Sagna heads clear.

82 mins: Lewandowski wins a high ball, brings the midfield into play, and Dortmund switch the ball right to substitute Aubameyang. Gibbs is drawn forward towards him, Grosskreutz attacks the space in behind Gibbs, and hits another deep cross towards Lewandowski. Sagna had cleared on the previous occasion, but this time he’s high up the pitch having been attacking, and Lewandowski volleys in.

Arguably, Grosskreutz is the least talented player of the 22 starters here, and equally as arguably, he was the worst performer on the night. Continually given opportunities to cross, he repeatedly made the wrong decision or played a poor ball – it took him several occasions to get it right.

However, he was still the game’s key player, because he constantly had space down the right. By the end of the game, he had covered 11.5 kilometres – which is the difference between the distance Arsenal ran, and the distance Dortmund ran: 106,281 metres to 117,887.

These numbers aren’t generally considered important, and Klopp famously commented that his side have improved since they started running less. But in the previous match, a win against Marseille, he said, “We had to put in a lot of effort and if we’d run just a few kilometres less today, we would have struggled.” Grosskreutz’s ‘distance covered’ statistic here neatly summarises his contribution – his stamina made the difference.

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