After Pep Guardiola left FC Barcelona last summer, players and fans worried openly about the ability of Tito Vilanova to effectively replace him as manager. Vilanova has proved this campaign, however, that not only is he an effective replacement for Guardiola, but his refreshed style has opposing teams once again guessing as to how to stop the Catalan side. 

Though Barcelona have already lost three times to Real Madrid this season, once in the Super Cup, once in the Spanish Cup, and once in La Liga, two of those three losses came while Vilanova was in New York receiving treatment for a resurgent cancer. Though Barcelona has at times been uninspiring this year, at times grinding out boring away wins, they still maintain a 13-point lead in the league, and have always come to play when it has really counted.

As such, perhaps the defining game of the Vilianova reign thus far came in the return leg against AC Milan in the Champions League round of 16 last month. With the Catalans having suffered a staggering 2-0 defeat in the San Siro, few observers expected a Barcelona side that appeared tired, deflated and simply out of ideas to be able to overturn the deficit. 

That night in the Camp Nou, however, Barcelona played that special, almost magical brand of soccer that they occasionally do. Dominating the game from the get-go, they played the kind of high pressure, tiki-taka soccer that causes even the likes of José Mourhino to shiver in his Valdebebas lair. Lionel Messi played at his brilliant best, scoring twice in the first half from outside the area, while Iniesta's darting runs stretched the Milan defense past its breaking point. 

Once the 4-0 score was finally confirmed, thanks to second-half goals from David Villa and Jordi Alba, many pundits once again listed Barcelona as favorites to bring home the European Cup. 

As far as I am concerned, UEFA might as well begin etching the name of the Catalan side into the Cup, as there will be no stopping them this year. 

Following the side's 2-0 loss in the San Siro, Barca midfielder Xavi noted, "This generation has yet to make a historic comeback and we'd like to do it. We owe it to the fans. We'll go all out to make a comeback." Having since then made that historic comeback, it appears as though little will be able to stop the Catalans this campaign. 

In last year's semi-final against Chelsea, Barcelona were still locked in dead heat for the league, having to play their best 11 every weekend in the hopes of catching Real Madrid. As a result, Barcelona's best players, Messi included, were simply unable to muster the energy necessary to play twice a week, every week. In the end, Chelsea won the final over Bayern Munich, at which point neither side had any chance of winning their respective leagues, thus allowing them to rest players to focus on the Champions League.

This year should pose no such problems for the Blaugrana, however, as Barcelona's comfortable 13-point lead in La Liga will allow them to rest key players ahead of their mid-week Champions League fixtures. 

Recognizing this opportunity, Vilanova has done a much better job of rotating and resting key players this year than Guardiola has done in years past, contributing heavily to their position in the league right now, even resting the tireless Messi from time to time. In addition, Barcelona has veered slightly away from their single strategy of attempting to pass the ball into the back of the net with every possession, something that teams were able to somewhat effectively defend against by packing their entire team in front of goal.

More importantly, this year Messi has been allowed even more free reign, attacking from all over the pitch, making it virtually impossible to man-mark him without leaving gaping holes in the defense. In addition, the more anarchic play of Cesc Fabregas, though off form as of right now, has given the Blaugrana the option to play more directly. Doing so has often allowed Barcelona to catch opposing teams napping, lulled to sleep by the metronomic passing of Sergio Busquets and Xavi Hernández.

The one area that has been suspect for Barcelona all year long, and which could ultimately be their undoing, is their defense. With Gerard Pique never looking like the world-class specimen he occasionally did under Guardiola, along with an aging Puyol, Barcelona have been unable to find a reliable center back tandem this season. In addition, the fact their two first choice fullbacks, Dani Alves and Jordi Alba, play more like attacking midfielders than defenders hasn't helped. More often than not Barcelona have conceded cheap goals as result of disorganized defending.

Much of the problem stems from the style of defending that both Pique and Mascherano, a defensive midfielder converted to center back out of necessity, foolishly employ. Both of them can be observed diving into tackles like their lives depend on it, when they would be much better served staying on their feet, dictating the direction of the attacking player. 

It has been suggested that this tendency to dive in is a result of arrogance, a belief that they will be able to make the decisive tackle every time. The habit both Pique and Mascherano have developed, however, is more likely a result of their fear that they will be beat for pace. Neither of them are particularly fast, and as a result, they feel as though they must dive in to stop a player before he can accelerate past them. 

Barcelona's defensive problems were most evident in the return leg of the Spanish Cup against Real Madrid. After only 12 minutes, Pique dove in rashly on Cristiano Ronaldo inside the area, with the referee rightly pointing towards the spot. In addition, time and time again the Catalans were cut wide open as a result of deep balls played in behind to Ronaldo, something that one would be forgiven for believing a Barcelona team should be able to effectively defend. 

So devastating were Ronaldo's runs in that game, in fact, that Barcelona never looked comfortable on the ball, having only a small sliver of their normally massive amount of possession. Despite their occasionally lackluster defense, however, Barcelona still lead La Liga by a wide margin, thanks in huge part to the most devastating attacking play in the world.

As Milan discovered in their 4-0 thrashing at the hands of Messi and company last month, Barcelona are still the most dangerous side in Europe. 

Every now and then, the argument is made that Barcelona is relying too heavily on the Argentine. Certainly, if Barcelona are to overcome their defensive vulnerabilities, they will need Messi to produce some of his trade mark magic, but relying on him to do so is not so far-fetched. Not only did he produce against Milan, but Messi has scored in his last nineteen league encounters, becoming the first player in history to score against every other side in La Liga in consecutive matches. 

Barcelona's chances of winning the Champions League this year, then, come down to the performances of one man. If Leo Messi produces the magic we all know he can, come May, Barcelona will be victorious in Wembley. Just as last year against Chelsea in the semi-final, when Messi's smashed penalty against against the crossbar caused Barcelona to be eliminated, his Barcelona teammates will be counting on him to make the difference. Given his current mindset, and barring an injury, expect him to do so. If he can, Barcelona will coast to a comfortable victory in La Liga, and win the Champions League, regardless of who they have to play along the way.

Reach staff writer Christopher Coppock here, or follow him on Twitter.