The first leg of Arsenal-Barcelona did not disappoint, with the Gunners stunningly coming from behind to win 2-1 three weeks ago at home in London.  So the return leg today in Barcelona is even more tantalizing.

As Fabregas indicated in his first leg post-match interview, one should think of these home&away aggregate-goal fixtures as a single 180 minute match. So Arsenal lead 2-1 at “half”; do they come out and try to defend that lead for 90 minutes on the road?  That is to say, will they attempt to park the proverbial bus?  Many believe Wenger is philosophically incapable of doing so, and he has said this week that Arsenal won’t do so–which perhaps mean they will?  It will be interesting to see the starting XIs Wenger and Guardiola will choose, the formations they deploy, and how they instruct their sides to play.

Both teams will be missing key players due to injury or suspension, requiring both managers to start players that haven’t done so most of the season.  Barcelona will be without both Pique and Puyol–the solid central back partnership for not only club but also World Cup-winning country.  So Barça will have a very different look in the back, which will most likely ripple into midfield.  Indications are that Guardiola will move Busquets back from his usual defensive midfield position to partner with Abidal in the center of the defense, and Mascherano will get the start in the holding midfield role.

Beyond that, Barcelona’s lineup should be consist of the usual suspects, arrayed in their usual 4-3-3: the Brazilian wingbacks (Dani Alves and either Maxwell or Adriano) on either side of the center backs; Xavi and Iniesta in the heart of the midfield; Messi, Villa, and Pedro providing the attack.

Though as tactical guru Jonathan Wilson described in a column last fall, it’s not unusual that both of Barca’s wingbacks go forward to provide width in attack–especially against sides that are sitting deep in a firmly parked bus–in which cases Busquets would drop back to stay home and keep Pique/Puyol company (and hence the 4-3-3 would morph to something more like a W-W, i.e.. a 2-3-2-3).

Two points to take away from that. One: central defense is not such a foreign place for Busquets. Two, watch for if/when the wingbacks get far forward, to see if Arsenal can regain possession and counterattack into that space.  That’s what Arsenal was able to do at the Emirates–most memorably on the beautiful winning goal, when Fabregas picked out Nasri behind the defense on the right wing, and Nasri waited for Arshavin to come up into the box up the right wing (running past a casually jogging Dani Alves).  But it also happened in the first half, when Fabregas and Walcott got behind the defense on two separate occasions.

Indeed, Arsenal could use Walcott on the pitch tomorrow, as his speed is something Barcelona is has worried about in previous matches. Unfortunately for the Gunners, he’s out due to injury, so it will fall to Nasri, Arshavin and most likely Bendnter to make those breaks forward, with Fabregas and Wilshere feeding them from the central midfield.  (Recall that in the 2nd leg of last year’s quarterfinals at the Nou Camp, Bendnter scored to put Arsenal up in the match and on aggregate–but shortly thereafter the Messi show started.)  Even though Robin van Persie was a late surprise inclusion in the squad, look for him to start on the bench and come on if Arsenal find themselves down.

The battle to watch is in midfield.  Arsenal is significantly without their defensive midfield stalwart Alex Song.  We expect it will be Abou Diaby to start alongside young Jack Wilshere as the two in Arsenal’s 4-2-3-1 (although Zonal Marking makes a case in his match preview that Wenger might go with Denilson).  If you can, simultaneously track Xavi, Iniesta, and Messi when Barcelona have possession (which should  of course be most of the time), and watch for who out of Barcelona’s midfield is able to track that trinity, tackle to regain possession–and potentially start counterattacks.