Chelsea vs Arsenal tactical preview: Beware Alvaro Morata, visiting defence has to do better and why Mesut Ozil injury is such a huge blow

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You wait all season for Chelsea against Arsenal and then two games come along in the space of a week.

Last Wednesday's thriller at the Emirates was one of the games of the season but both managers will be hoping to learn lessons from it, with each of the sides having arguably thrown away a win.

Sportsmail has taken a look at some of the tactical lessons that came out of the match last week and what each side needs to do better.

Arsenal's defensive line - and Mustafi - needs to be better

Arsene Wenger has flitted between a three-man defence and four at the back at various points this campaign.

It means there has been an element of confusion over the duties that each of his defenders has to fulfill. Never has this been more obvious than during the game against Chelsea last week.

The three-man Arsenal back-line were caught out repeatedly in the opening 15 minutes at the Emirates and Chelsea should really have gone at least a goal ahead.

Shkodran Mustafi was the culprit on both occasions, leaving the ball or standing in the wrong position.

Eden Hazard was let loose - a dangerous mistake to make - because Mustafi played him onside. And then Alvaro Morata could break through as Mustafi ignored the ball.

His struggles simply highlighted the fact that Arsenal's defenders weren't really sure what to do. Confusion was the name of the game.

Arsenal's defence was caught out with poor positioning twice in the first 15 minutes last week

Shkodran Mustafi was the real culprit, misreading the rest of the line and misjudging passes

Bellerin has to curb his forward momentum against Hazard

Admittedly, Hector Bellerin scored the equalising goal last week. He is also generally tasked with providing attacking width on the right.

The problem is that he is up against one of the Premier League's top creative talents in Hazard. In the last game Hazard found far too much space to exploit against the Gunners. 

With a three, the right centre-back should be able to shut him down. But Hazard is no normal player, and he probably needs Bellerin to double up on him to stop his threat.

More discipline is therefore required from the Spain international. 

Hector Bellerin has to stay back and ensure Eden Hazard is not left in acres of space again

Mesut Ozil's absence is a huge blow 

If Chelsea wanted to limit Arsenal's threat on Wednesday night, they needed to do one thing well - shut down Mesut Ozil.

The debate surrounding the German has been ongoing throughout his Arsenal career. But last week he was integral to any attacking threat the Gunners had going forward.

They only managed to create six chances for themselves, which suggests an issue creatively. And of those six, three were crafted by Ozil.

And now that he has been ruled out of the game with injury, it means there is much less for Chelsea to contend with. 

Mesut Ozil was Arsenal's top creative threat last week - his absence is a huge blow to them

Beware Alvaro Morata

One of the major tales from the game at the Emirates was Alvaro Morata repeatedly spurning what seemed like clear chances in front of goal.

Three times he was left one-on-one with Petr Cech. Twice he hit the ball wide of the right post. During one of the last attacks of the game he hit a half volley directly at the goalkeeper.

It led to jokes about his lack of ability with his feet compared to his head, but Arsenal will need to be wary on Wednesday.

If his movement and Arsenal's lax defending provides him with the same chances again, he's not likely to come away from Stamford Bridge without his name on the scoresheet.

Alvaro Morata is very unlikely to pass up as many goalscoring opportunities this time around

Marcos Alonso gets forward... so mark him

Again, there were jokes about Marcos Alonso being a better striker than Morata after his goal last week.

The defender has a ludicrous record in front of the net for a left-back, but generally speaking those goals are not poacher's efforts in the same manner as his strike against Arsenal.

It seemed like it was a concerted effort from Alonso and Antonio Conte to get the defender into that position. He could be regularly found in the final third when crosses came into the box.

Arsenal need to pay attention to him and his runs into the area. 

Marcos Alonso scored for Chelsea last week after a late run into the box to put his side 2-1 up

But he made those movements throughout the game and cannot be ignored again

Alonso has one of the best goalscoring records of any defender in the Premier League

Tighten up, Arsenal

The four best games of the season have taken place at the Emirates - the matches against Leicester City Manchester United, Liverpool, Chelsea.

That is primarily because Arsenal have lost any sense of defensive organisation and are now utterly willing to play end-to-end football.

Arsenal let their opponents have 19 shots at their goal last week.

They cannot do the same at Stamford Bridge. Chelsea will not be as loose themselves on their home patch. And surely they will be more clinical.

Potential line-ups

Chelsea XI: Courtois, Azpilicueta, Christensen, Cahill; Moses, Kante, Fabregas, Bakayoko, Alonso; Hazard; Morata

Arsenal XI: Ospina, Mustafi, Holding, Chambers; Bellerin, Xhaka, Wilshere, Maitland-Niles; Sanchez, Welbeck; Lacazette

Chelsea's key man Hazard is almost nailed on to start at Stamford Bridge on Wednesday