In a competition famed for giant killings and upsets, it's rare to reach the FA Cup semifinal stage and find four genuinely top sides remaining in the hunt.
Chelsea, Tottenham, Manchester City and Arsenal represent four of the Premier League's top six, and Saturday's semifinal is a meeting between the top two. Chelsea and Tottenham are England's best two sides this season, and their meeting will be a fascinating battle of tactics and technique.
These two have emerged as outstanding sides primarily because of their system as much as their individuals; you think of Chelsea and consider their 3-4-3 system, you think of Tottenham and consider their aggressive pressing. But in reality, both Antonio Conte and Mauricio Pochettino have found the right balance between a structured system and allowing individuals to express themselves, and a perfect example is the way both managers have accommodated two talented No. 10s in otherwise highly systemised sides.
For Conte, the change of system was paramount. The Italian tactician arrived at Stamford Bridge last summer intent on playing a 4-2-4 system, and then modified his intended shape and switched to a 4-3-3 system, somewhat familiar to Chelsea over the years. Both those systems featured two wingers, with Eden Hazard in a wide-left position. The switch to 3-4-3, however, allowed Hazard considerably more freedom.
The Belgian is still notionally Chelsea's left-sided attacker, of course, but the change of system means he operates far more in central areas, with Marcos Alonso flying down the outside. Indeed, prematch television lineups never know entirely whether to depict Chelsea in a 3-4-3 or a 3-4-2-1, such is the tendency for Hazard and Pedro to take up narrower positions to allow the wing-backs to fly forward and form a front five.
From there, Hazard has acted as a playmaker as much as a pure attacker. Chelsea lack a defined midfield creator when Cesc Fabregas has been omitted, as has been the case for much of the campaign, and it's therefore Hazard who has taken charge, running games from central positions as well as providing the difference in the final third.
The role of Pedro, too, has been interesting. Throughout his career the Spanish international has generally been considered a wide forward rather than a playmaker, and a goal scorer more than a provider.
But in this system he increasingly has darted into positions between the lines rather than sprinted in behind, and managed seven assists in addition to seven goals, demonstrating how he's both playing the penetrative passes and providing the finishing touches. Although not involved in play as regularly as Hazard, Pedro is effectively his side's second most creative player -- again, when Fabregas is absent -- which is a new role for a player accustomed to playing in teams overloaded with creative talents.
Tottenham, meanwhile, have done something very similar -- occasionally in a 3-4-2-1 system somewhat similar to Chelsea's, but also in a 4-2-3-1 system. They have more of a pure playmaker, Christian Eriksen, usually darting inside off the right flank. Whereas Hazard is arguably an attacker and arguably a winger, Eriksen is a more natural No. 10, the type of player a slower-tempo, more patient team would build their attacking play around.
Tottenham do not build their attacking play around Eriksen, however. With Tottenham, his role is drifting inside, slightly on the periphery of the action, and playing clever through-balls into onrushing attackers. In a sense he's slightly sidelined.
The reason, of course, is that Tottenham can also count upon the precious talent of Dele Alli, another brilliant attacking midfielder, but yet another completely different type of playmaker. Alli is more of a space invader than a creator, someone who looks to cause havoc with his late running in beyond lone striker Harry Kane, rather than someone who drops deep into midfield to dictate play. Indeed, while sometimes fielded deeper in midfield or occasionally out on the left by Pochettino in his first Spurs campaign, Alli has been shifted increasingly farther up the pitch, and into zones where he essentially has become a second striker.
Of course, the combination of Eriksen and Alli's different styles was precisely what allowed Tottenham to unlock Chelsea's defence the last time they met, in Tottenham's comprehensive 2-0 victory back in January, when Conte's side had previously looked almost unbeatable.
Pochettino replicated Conte's 3-4-3 system, used Eriksen drifting inside from the right and Alli storming forward from the left. Spurs' two goals were almost identical; Eriksen exploited the space in front of Gary Cahill, dinked a cross over the Chelsea defence for Alli, who rose above Cesar Azpilicueta to head home. It's rare to see two such similar goals in the same game, although that combination isn't necessarily representative of Spurs' play. Eriksen has assisted Alli on only one other occasion this season but has set up both Harry Kane and Son Heung-Min for goals on four occasions each.
The key to Saturday's semifinal will probably be about how often the sides can work the ball into these players between the lines. Neither are blessed with much outright creativity in conventional midfield positions, with the pairings of N'Golo Kante and Nemanja Matic, and Victor Wanyama and Mousa Dembele, largely being about mobility, physicality and ball-winning quality rather than incision. Indeed, it's arguably that there's more ball-playing expertise from David Luiz and Jan Vertonghen.
Therefore, it may largely be about spatial awareness and footballing intelligence from the aforementioned four playmakers -- how much can they get on the ball and influence the game? On the back of Hazard's inability to escape man-marking at Old Trafford last week, the sense that Tottenham's defence is a currently a tighter unit than Chelsea's, and the cleverness of Spurs' two goals against Chelsea last time, Pochettino's side might well be favourites.