Champions League key matchups: Pepe, Morata, Thiago and Neymar

The 2014-15 Champions League may have been something of a slow burner so far, but the quarterfinal stage has delivered four ties of the highest quality. A rematch of the 2014 final awaits in the form of the Madrid derby, while the pairing of Juventus and AS Monaco means that at least one of the less-fancied teams will make it to the semifinal stage.

Paris Saint-Germain against Barcelona throws together two managers looking for their first success in Europe, while FC Porto vs. Bayern Munich is a battle of two of football's great young minds, Pep Guardiola and Julen Lopetegui.

None of the ties look particularly easy to predict, but there are a few individual confrontations that should have a decisive sway on the outcome of the round.

Antoine Griezmann (Atletico Madrid) vs. Pepe (Real Madrid)

The last Madrid derby wasn't a particularly pleasant one for the Champions League holders. Atletico's 4-0 win at the Vicente Calderon on Feb. 7 wasn't only surprising because of the scoreline, it was also striking in terms of how dominant the home team were. Not only did Real Madrid ship four goals, they were also completely outplayed, with Diego Simeone's team producing impressive passing combinations that showed they are capable of being more than just a counterattacking outfit.

Much has changed since then, however, not least Real Madrid's injury situation. Luka Modric, James Rodriguez, Marcelo, Sergio Ramos and Pepe all missed the February derby, and all are likely to appear on Tuesday.

The last name in particular could be a significant difference-maker this time around; whisper it softly, but Pepe has quietly become Madrid's most reliable defender over the last few seasons, ditching the rage of old for a commanding maturity that is invaluable to his team. When the Portugal international misses a game, Real Madrid feel his absence.

The centre-back's biggest concern in the quarterfinal will be Atletico's most consistent player this year, Antoine Griezmann. The Frenchman has provided the Colchoneros with sustenance through their difficulties of late, scoring four goals in his last three league fixtures, and proving that he has completed the transformation from wide player to central striker.

Pepe vs. Griezmann should be a fascinating battle to witness. The Portuguese may be taller but both are good in the air; the Atletico man is quicker but the defender has better positional awareness than many give him credit for.

The last time the two faced off, Griezmann came out the better of the two, pouncing on a Pepe error to assist Fernando Torres in the Copa del Rey last 16. The victor of the duel this time around could be equally important to the scoreline in their Champions League battle.

Alvaro Morata (Juventus) vs. Ricardo Carvalho (AS Monaco)

Real Madrid were well aware of the kind of potential they lost when Alvaro Morata moved on last summer, but even his old club must be surprised by the consistency the young striker has found since the turn of the year.

Despite never before playing regular top-flight football until this season, Morata has taken to the highest level like a duck to water, nudging far more experienced compatriot Fernando Llorente down the pecking order at Juventus and endearing himself to both the Old Lady's support and Massimiliano Allegri.

An intelligent striker who thinks a great deal about varying his movement in order to surprise opponents, he came away with two goals and an assist from Juve's last 16 clash with Borussia Dortmund. Should Monaco overlook his threat in favour of focusing on Carlos Tevez, they too may find themselves on the receiving end of the Spaniard's quality in front of goal.

Ricardo Carvalho, who will remember Morata as a promising Real Madrid Castilla player from their time together in the Spanish capital, offers Monaco some unique insight into the striker. Carvalho was on the pitch when Morata made his Madrid debut against Real Zaragoza in 2010, and having trained alongside the striker, may be the Monaco defender best positioned to effectively nullify his qualities.

Age may be taking its toll on the 36-year-old's body but his experience will be invaluable. The Champions League is the competition Carvalho made his name in over a decade ago, when he lifted the trophy at Porto. Morata will need a big performance against the veteran to try to similarly establish his own name among Europe's elite.

Casemiro (FC Porto) vs. Thiago Alcantara (Bayern Munich)

The midfield is always of huge importance in football but for two coaches as obsessed with that area of the pitch as Pep Guardiola and Julen Lopetegui are, the rule will apply to an even greater degree at the Estadio do Dragao on Wednesday.

Bayern evidently have the edge in terms of star quality but Porto have plenty of class of their own, and two young midfielders in particular have the potential to influence the outcome of the tie.

Bayern's comically bad injury record this season leaves them without David Alaba and Javi Martinez as potential options for the middle, while Bastian Schweinsteiger is a doubt and at the minimum won't be 100 percent fit. Franck Ribery and Arjen Robben, two incredibly important creative influences, will also miss the trip to Portugal.

In those circumstances, a player of Thiago Alcantara's passing quality cannot be ignored, even if he has only just returned from a yearlong battle with injury himself. An excellent display against Eintracht Frankfurt on the weekend made an even stronger case for his selection in Porto: the delicious chipped pass Thiago produced in the build-up to Robert Lewandowski's opener is exactly the kind of spark Guardiola will be looking for in a key Champions League game.

Space is required to produce a killer pass, however, and Porto's midfield shield Casemiro will try to keep things tight while sitting in front of the home back four. The on-loan Real Madrid man produced an impressive cameo for his parent club against Borussia Dortmund at this stage of the Champions League last year, seemingly unfazed by the occasion, given how tidy he was under pressure.

Not only physically robust enough to put in the miles necessary to frustrate Thiago over 90 minutes, the Brazilian also has enough talent of his own to use the ball well when given the opportunity. Bayern will need to be wary of Casemiro's shot from distance after the stunning free kick he scored against Basel in the last round.

Marquinhos (Paris Saint-Germain) vs. Neymar (FC Barcelona)

Lionel Messi's threat for Barcelona is so obvious it almost isn't worth mentioning, and there is little doubt that Laurent Blanc will have put in plenty of hours instructing PSG on how to limit his influence. Focusing on Messi inevitably leaves space for other players to cause problems, however, and that's where Neymar will be particularly important for the Catalans at the Parc des Princes.

Against Sevilla on Saturday the forward delivered his best performance in months, assisting Messi's opener, curling away a beautiful free kick for the second goal of the game and producing a nutmeg on Nico Pareja that merits rewatching. Visibly displeased with being substituted off in the second half by Luis Enrique, the forward will have a point to prove in the Champions League, and that's bad news for PSG.

The absence of David Luiz through injury means fellow Brazilian Marquinhos is the central defender most likely to come into contact with an agitated Neymar. Playing the entirety of PSG's Coupe de la Ligue final win over Bastia should give him a helpful dose of confidence, but silencing Barca's No. 11 is a different challenge altogether.

Marquinhos hasn't played at centre-back as often as he would have liked this season thanks to the addition of Luiz, so Wednesday is a golden opportunity for him to show Blanc what he's capable of. If Barcelona are still watching the defender as they have been for a few years now, then it could be a chance to further impress them, too.