Strike partnerships with a difference: why are split forwards so popular and what advantages do they offer? 

At Barcelona, Henry revealed, Guardiola would ask him and Samuel Eto'o to position themselves next to the opposition full-backs in order to 'pin' the entire back four. Wary of their darting runs in behind, centre-backs would not push out thus allowing Barcelona to out-number their opponents in other areas and establish one of their familiar dominant spells of possession. 

"Stay in your position, trust your team-mate on the ball, and wait for the ball. Look at where I am (hugging the left touchline). That position allowed (Andres) Iniesta to get the ball (in central midfield) because I’m occupying the right-back," Henry said. 

In layman's terms, the aim is to 'keep them honest' and wary of committing too many bodies forward. A top-class centre-back pairing might back themselves in a straightforward two-against-two, but if the forwards are occupying false positions that drag them wide they might be less confident and ask their full-backs to stay at home. 

Here is one example from Arsenal's 2-0 win against United, when Pierre-Emerick Aubameyang and Alexandre Lacazette lead the line at the front of Unai Emery's 3-4-1-2. Arsenal's two forwards break into both channels, dragging United's back four with them and leaving half a tennis court for Mesut Ozil to receive the ball in. Ozil slows the attack slightly, and United actually do well to recover and concede a corner. 

Minutes later though, Arsenal took the lead. Granit Xhaka's strike and David Ge Gea's misjudgement was an isolated incident but again we see the same pattern in the move that led to it: lots of Man Utd players occupied but not marking anyone, and that creates oceans of room for Arsenal's midfielders to collect the ball just outside the area. Had it not been Xhaka, it would have been Ramsey.  Lacazette has pulled all the way to Luke Shaw's outside in this example. 

Solskjaer deserved some credit for switching to three centre-backs rather than a flat four after 30 minutes, and from then on United had a better grip of both Arsenal's forwards and the game.

Counter-attacking behind advanced full-backs 

The reciprocal of the first problem: rather than the forwards pinning the full-backs to help midfield establish control, they can punish them on the counter when they do advance. 

Son's second goal at the Etihad in the Champions League came from this scenario. Guardiola devotes hours of time and energy devising ways to ensure City are not caught on the break, having had his fingers burnt by Liverpool, Atletico Madrid and Real Madrid in previous Champions League exits as a manager. This can include having his full-backs inside next to Fernandinho and stopping the opposition with tactical fouling (something he was keen to deny). 

Unfortunately, Guardiola's best laid plans could not account for Aymeric Laporte suddenly taking a Sunday league touch on which Lucas Moura pounced. On the other side of the pitch Kyle Walker was getting ready to join the attack, only to find himself the wrong side of Son and sprinting back. Walker does get back goal-side but with City's defence in rapid retreat, Son wrong-foots them by checking back and whipping the ball into the top corner with his right foot. Nothing tactical there, that's all about the quality of a devastating forward. 

A small irony is that it was Tottenham who were on the wrong end of this dynamic earlier in the season. Mauricio Pochettino has favoured a diamond in the bigger games, with bodies packed into the middle of the pitch ready to aggressively counter-press when they lose possession. Everyone loves a 4-4-2 diamond because it's a good way of getting all your best players on the pitch (one reason it was favoured by Sven-Goran Eriksson with England who never wanted to leave out a star). 

One potential problem though is the reliance on full-backs for width: you cannot really play it without asking them to go forward. Manchester United exploited this in their 1-0 victory at Wembley, with Paul Pogba spinning a wonderful pass into the space behind Ben Davies who is barely in the frame (top right). Marcus Rashford did the rest with a fine finish across Hugo Lloris, in the days when Solskjaer could do no wrong. 

Emery also used this approach in Arsenal's stirring second-half comeback in December's north London derby at the Emirates, with Lacazette and Ramsey introduced at half-time. Arsenal's second and third goals in a 4-2 win came from early passes into the channels as Lacazette and Aubameyang dragged Tottenham's back four around. 

Pressing teams who play from the back

Sucking teams in in order to create space higher up the pitch is one reason why teams are trying to play out from the goalkeeper, and having two forwards can disrupt and deter this approach.

Split strikers can be particularly effective because they are in a position to close down a short pass to the centre-back or cut off the longer pass to a full-back. If the strikers marked the centre-backs touch-tight, it would be simple for almost any Premier League goalkeeper to just chip the ball over their head. When a team plays with split strikers they normally have an advanced midfielder or false nine just behind them, and it is his job to drop onto the opposition's holding midfielder or chief playmaker. 

Chelsea and Jorginho have struggled to find ways around this in big away games with Spurs and Arsenal both using a midfield diamond and front two to blitz them before half time. 

Here is a textbook example of how Arsenal set up whenever Chelsea had a goal kick, with Ramsey pushing on to Jorginho and Aubameyang (on the left in this case) splitting the difference between Antonio Rudiger and Cesar Azpilicueta, who also had Mateo Guendouzi at his tail. A good first-time pass and some nice footwork from N'Golo Kante won Chelsea a free-kick and saw them evade the pressure. 

In the below instance at Wembley, Dele Alli shadows Jorginho behind Tottenham's front two of Son and Harry Kane and cuts off the pass into him. 

Chelsea visit Old Trafford on Sunday, and United could adopt a similar strategy with Jesse Lingard buzzing around Jorginho and Rashford and Martial as the split strikers.

Similarities with Liverpool's front three 

Jurgen Klopp's Liverpool line up with a front three on paper, but in the course of a match Mohamed Salah and Sadio Mane can also resemble a pair of split strikers. Roberto Firmino drops into a number 10 position looking to draw out defenders, with Mane and Salah making runs into the space he vacates between centre-back and full-back. Although they hardly ever wavered from a 4-3-3, Guardiola's best Barcelona teams did something similar with David Villa and Pedro staying on the last line of defence and Lionel Messi free to drop into midfield from a nominal centre forward position. 

Squad building short-cuts

Few teams wish to play with two strikers in every game across a long season. Therefore, possessing a stable of forwards such as United's treble-winning quartet of Yorke, Cole, Sheringham and Solskjaer is not only unlikely but quite possibly undesirable. It would be extremely difficult to keep four conventional strikers happy, and they would command a huge chunk of any wage bill. 

Having one or possibly two headline strikers supported by a couple of multi-functional attackers is more sustainable. Typically these players - such as Son - started their careers as wide players and so playing with split strikers suits their natural instincts. If the coach decides to change tack in the next game, they can shift back out wide without any issue and this saves having to carry (and pay) a different player for each role.