If a home win for Chelsea against Barcelona seemed improbable last week, getting a result at Camp Nou is surely impossible. Before that defeat to Real Madrid in their last game, Barcelona had won eleven consecutive games at home. With Chelsea’s poor away record in the Champions League this season and Barcelona’s utter domination of world football in the last four years, it is almost laughable to envisage a scenario that does not end in a Barcelona triumph. But surely there is a case to be made that provided certain — albeit inconceivable — factors align, Chelsea may come away from the second leg game with little more than just an ego-boosting first leg win.

Pep Guardiola has tinkered with his Barcelona side a lot recently, sometimes even playing three at the back with a midfielder in Javier Mascherano or Sergio Busquets occupying a centre back role. He has done this partly to deal with injuries but also, it seems, to try and challenge a team that has shown a relative lack of motivation this season. That is quite understandable for a team that has won two out of the last three Champions League titles and the last three La Liga titles in grand style. They are now easily one of the best teams of all time, but for all their pretty play this season, there is a carelessness and complacency that has crept into their game. This has been particularly visible in their last two games, where they have created chances aplenty but seem lackadaisical about putting them away. Even though they are still the best team in the world, they lack the cutting edge and the desire that they showed in previous seasons and Chelsea will need to exploit that to the fullest. This might be the last chance for some of their ageing key Chelsea players like Frank Lampard and John Terry to win the Champions League and they need, more than anything, to show that they want it more than Barcelona do.

Despite a 1-0 deficit and Pep Guardiola’s comments to the contrary, Barcelona is still favorites to go through, but minor cracks are beginning to show in the armour of what is still a colossal juggernaut. They have now lost two games in a row, to Real Madrid and a Chelsea side that through a combination of stoic defending and a massive amount on luck, were able to keep the Barcelona onslaught at bay. That clean sheet at home will be just as crucial as Didier Drogba’s 45th minute goal to any hopes they might have of progressing to the final. A goal for Chelsea at Camp Nou will mean the Catalans will have to score at least three goals to progress, a fact that is surely not lost on either team. Chelsea have scored first in all their Champions League ties this season, and they will need that run to continue.  It is vital that they score that first goal and also keep Barcelona out for as long as possible to give themselves a realistic chance of progressing. Concede early and the tie is practically lost, but prevent the home side from scoring for long enough and sooner or later the fans will get nervous, which might translate to nervous play on the pitch by the Spanish giants.

Another important factor could be fatigue. Both teams had very important games at the weekend, but while Chelsea were able to rest key players with Ivanovic, Cole, Lampard, Ramires, Meireles, Mikel and Mata all sitting out, the only changes Guardiola was able to make for El Clasico was to place the misfiring Sanchez and Fabregas on the bench beside him. If Barcelona’s players are tired, it could mean that they might not be able to sustain as high a tempo as they want, and might not be able to make as many off the ball runs as they normally do – factors which are key to their style of play. Chelsea’s ability on the other hand, to rest key players in their full back and midfield positions could mean they are fresh and ready to work even harder on Tuesday. This is important, as away from home they do not have the crowd on their side, and will need every ounce of concentration and hard work they can muster. The game can easily be lost by silly decision making, particularly in the 18-yard box, and their extra rest might help prevent that.

Someone that has made many a player look foolish in that penalty area is Lionel Messi, the most dangerous man on the field, and someone that Chelsea will have to try and shackle at the Nou Camp. That is obviously easier said than done, because this is a player who at 24 should already be in every reasonable list of the best players of all time. He already has 63 goals and a Champions League record 14 goals this season, and will be looking to add at least one more on Tuesday night. However, he is also on a two game goal drought, which is apocalyptic by his standards. In the first leg Chelsea was able to restrict him to just long shots which they blocked effectively. He looked somewhat frustrated, constantly dropping deep to get the ball and trying to set up his teammates who consistently fluffed their lines in front of goal. That being said, he has had two average games in a row, including that first leg against Chelsea, and they will need him to have an improbable third to have any hope at all of playing at the Allianz Arena next month.

Chelsea will also need to show the same sort of grit and steely resolve that they displayed in the first leg in order to come away from the Camp Nou with any sort of result. They will need to play to their strengths, exploiting their height and strength advantage in dead ball situations. Branislav Ivanovic’s long throws seemed to bother Barcelona a lot in the first leg, and that is a weapon they should look to use more away from home. Chances will be few and far between, which means they will also need their key players to turn up. John Terry and Frank Lampard were immense, but it was Didier Drogba that stood out in the first leg, with his hold up play and high work rate pivotal to victory at Stamford Bridge. Say what you will about his theatrics, but all that rolling around on the floor was crucial in stemming Barcelona’s flow, disrupting their rhythm and buying his teammates a few seconds of rest from chasing the black-clad shadows from Catalonia. Without his power and playacting, Chelsea could struggle. Enter Fernando Torres, who will undoubtedly be his replacement, to provide a different sort of threat. He will add pace to the counterattack and even though he has had a lacklustre season, while he was at Spain with Atletico Madrid he scored seven goals in five different matches against Barcelona. Chelsea will be content with just one of those goals on Tuesday night.

Finally and most importantly, Chelsea will need some of the luck that has eluded them in previous Champions League ties with Barcelona. The 2009 semi-final in particular still hurts them, and they will be looking to put that particular ghost to bed once and for all. They will need to be unified, to display a level of unselfishness, sense of purpose, organisation, belief and urgency that has been lacking from their play all season. Then, and only then, will they have any chance of completing the good work they started in the first leg and booking that May 19th ticket to Munich.