Manchester City's lead at the top of the table is still eight points but another narrow victory has given the chasing pack some hope.

An excellent tactical change at half-time against West Ham United ultimately handed victory to Pep Guardiola's team, but it might not end the same way when they face rivals Manchester United next Sunday.

Jose Mourinho's team are looking far more fluid in their new 3-4-1-2 formation, while Liverpool scored five goals in an unusual system of their own at Brighton. Elsewhere Big Sam got off to a winning start with Everton and Newcastle United's tactical experiment failed at Stamford Bridge.

Here are three things we learnt from the weekend action:

1) Man Utd's new 3-4-2-1 formation is the perfect solution to their attacking problems

For four years Manchester United have struggled to consistently play high tempo football and instead have often looked too flat, too wide in their formation, and too static in their attacking patterns. Jose Mourinho has finally discovered the solution to this problem: playing a 3-4-1-2 formation that provides closer support to Romelu Lukaku.

Firstly, United's width is more structured thanks to the deployment of wing-backs in this formation, as both Ashley Young and Antonio Valencia could commit to attacks safe in the knowledge that their centre-backs would cover. But more important was the use of Jesse Lingard as a number ten behind Lukaku and Anthony Martial, who played side-by-side up front. Having three players in central areas, rarely more than ten yards apart, created some excellent counter-attacks – including the build-up for all three United goals.

However, using Paul Pogba and Nemanja Matic in a two-man midfield is the one downside to this system. A weakness in the centre allowed Arsenal to pour through the middle and amass 33 shots on goal; it is a blessing in disguise that Pogba will be suspended for the Manchester derby next weekend.

2) Guardiola's second-half reshuffle shows that, with De Bruyne in the team, outwitting Man City is almost impossible

West United defended superbly on Sunday and added important knowledge to a building resistance against Man City's slick attacks. Instead of pressing the City players as they entered the final third, David Moyes's team refused to make any tackles at all, meaning they were not pulled out of shape by the runs of Raheem Sterling or Leroy Sane.

Crucially, their midfield sat in front of David Silva and Kevin de Bruyne, cutting off the passing line to these two and consequently denying City their usual route to goal. West Ham deserved to go into the break 1-0 up, but a big tactical shift at half-time swung the game decisively in the hosts' favour.

Guardiola brought on Gabriel Jesus and played in an aggressive 4-2-4 formation, forcing West Ham to retreat alarmingly as they tried to cope with the numbers in the City attack. More importantly, De Bruyne was moved into a much deeper role, which meant he got on the ball a lot more and started pulling the strings from deeper. The Belgian had 43 touches of the ball in the first half and 87 in the second, reflecting his growing influence before that perfect cross for Silva's winner in the 83rd minute.

3) Rooney, Sigurdsson, & Calvert-Lewin will be the key players to instigate Big Sam's tactics

Successive clean sheets and six points in four days has lifted Everton to within seven points of seventh, meaning they are surprisingly close to their target position for the season. Sam Allardyce's defensive coaching has clearly already taken effect, and in the win against Huddersfield Town on Saturday we saw exactly how they will look to attack with Big Sam at the helm.

Wayne Rooney continued to play in central midfield, a position he will thrive in under the new management. Allardyce has always used a central midfielder capable of firing long, accurate balls into the channels (such as Mark Noble, Yohan Cabaye, and Kevin Nolan), and Rooney is the perfect experienced player to do this at Goodison Park.

Gylfi Sigurdsson was much better playing from the left, using his superb crossing ability to good effect against the Terriers, while Dominic Calvert-Lewin was superb once again. His runs in behind and strength when holding up the ball in the channels will be crucial for winning set-pieces as Allardyce instigates a direct system. Together, these three players hold the key to an Everton revival.

Best of the Week – Liverpool's versatility

Tactical versatility isn't something we associated with Liverpool in the 2016/17 campaign but the addition of Mohamed Salah has given Jurgen Klopp more options in attack while injuries have forced him into some successful experiments in defence. This week, Georginio Wijnaldum and Emre Can were surprisingly effective as centre-backs in a 3-4-3 formation.

Trent Alexander-Arnold deserves the plaudits for a tremendous performance from right wing-back that assisted the converted midfielders, but an even bigger help was the speed and fluidity of the Liverpool attack, which pinned Brighton in their own half. Klopp's front three is surely the best in the country; Liverpool are one centre-back and one Naby Keita away from being title contenders.

Worst of the Week – Benitez's chaotic tactical experiment

Rafa Benitez chose to play with a flat back five for the trip to Chelsea, as many managers do, but his side's messy defending suggests not enough work was done on the training pitch to make this system change a good idea.

Newcastle United looked sloppy throughout the match, leaving players unmarked, leaving huge gaps in central midfield, and pressing sporadically - pulling themselves out of their 5-4-1 shape. All three Chelsea goals came from needless defensive errors, while Eden Hazard pulled the strings by easily staying away from Newcastle players.