At the start of the game, Arsenal attempted to pressure Chelsea’s back three on the ball. Iwobi would push high and try to close down Azpilicueta from the outside, but Azpilicueta was still able to find passes to Moses. In doing so, Chelsea had good opportunities to create with the typical around-the-corner diagonal pass from the wing-back to the frontline. Willian dropping next to Moses would take Elneny away from Arsenal’s backline, leaving a great deal of space ahead of their backline (Xhaka and Wilshere still recovering from the high press) to create a 3v3 situation—Pedro, Hazard, and Alonso (joining) against Bellerin, Koscielny, and Mustafi.
Moses’s pass in that case (just a few seconds into the game) was not accurate enough, but as Chelsea continued to draw pressure on the ball from Arsenal’s midfielders, they kept leaving space in midfield for Chelsea to keep creating such chances, eventually leading to them taking the lead.
Build-up for the goal started once again with Azpilicueta, who drew Xhaka towards him with his body open and looking to play the ball to Moses, but then turning back inside and finding Kante free instead. Kante travels forward and looks to play the ball to Willan, drawing both Mustafi and Elneny towards Willian and away from where Kante would eventually play the ball—Mustafi moving towards Willian was also a side-effect of Monreal initially moving out wide to close down the space to Moses. The space vacated by Mustafi is where Hazard, after feinting for Kante’s pass, runs into and where Pedro finds him with a through ball.
Without the ball, Chelsea defended with a much higher backline than usual and tighter lines in midfield, where Chelsea would look to pressure the ball as Arsenal moved into the middle third. Maintaining pressure in midfield (while holding a high line) was important in order to prevent Arsenal from having time and space on the ball to exploit the space behind the back three. Chelsea drew Arsenal offside 10 times in the game, showing good anticipation, while recovering well on longer passes behind that had more “hang-time”.
In the few moments when Arsenal made it into the final third, they were able to create problems with midfield runs off the back of Chelsea’s midfield line and into the gaps between Chelsea’s backline—Iwobi’s diagonal pass finding Wilshere joining the box and forcing a save from Caballero. Arsenal could also use Bellerin’s pace advantage on the outside to get behind Alonso with the ball and put crosses into the box, one of which led to a corner and Arsenal’s equalising goal—the first goal Chelsea have conceded from a corner played directly into the box this season.
After equalising, Arsenal’s approach changed. They put less pressure on Chelsea’s backline with the ball, Iwobi dropped deeper to cover Moses more consistently, and the central midfielder stayed tighter to their backline in order to control the space between the lines.
Chelsea’s wide central defenders were thus able join the central midfielders with a high amount of possession in midfield and the final third. They moved the ball from side-to-side to look for openings—Willian made a few diagonal runs behind the defence upon Rudiger receiving the ball in space, but those passes were rarely risked.
Moving side-to-side but unable to create in the middle, Chelsea needed their wide players to dribble or find passes inside in order to open up Arsenal’s defence. Moses had another bad performance in this regard, where he was unable to beat Iwobi consistently enough in order to put crosses into the box. From the left, Alonso could attempt the usual combinations with the forwards, keeping the ball wide and high (and slightly deeper). Pedro moving wide and Alonso switching created the opportunity for Willian, when Hazard allowed Pedro’s early diagonal pass to run past him. But Chelsea were unable to isolate Pedro 1v1 on the wing, with Bellerin was very aggressive and quick to push up and pressure Pedro’s first touch.
Willian’s injury then cased Chelsea further problems, especially since Barkley, understandably, didn’t produce a great performance. He’s yet to have enough time to work on the movements and combinations between the front three, as well as still trying to learn how to play for Chelsea both in the front three and a midfield three (same as with Bakayoko taking months to adapt to playing in different roles in both formations).
Without the combinations and movements between the front three, Hazard switched his style of play, and started looking for runs and spaces wide of Arsenal’s defence. Mustafi and Koscielny showed great aggression and intensity in pressing him when he received the ball wide, winning the ball on a couple occasions, fouling on several others ... and getting beaten on the dribble a few times as well.
Wenger made a big tactical change at half-time, switching from a back-four to a back-three, with Elneny dropping between the central defenders and marking Hazard (later Batshuayi). This allowed Koscielny and Mustafi to play wider and focus more on pressing Pedro (later Hazard) and Barkley. Furthermore, it allowed Monreal to move out wide to cover Moses (later Zappacosta) on the wing and free up Iwobi of his defensive responsibility, where he could stay higher up the pitch and provide support when Arsenal won the ball.
Arsenal also had a great deal more possession, and were able to find players between the lines to push back Chelsea’s backline. Chelsea’s midfielders were unable to sustain the pressure across the pitch to remain high up.
Although the dominant team in terms of possession had changed, the best chances still came from counters. Chelsea had chances through winning the ball in midfield and finding Hazard to dribble or run behind. After Arsenal’s defensive shift, there were also more spaces wide of their backline for Chelsea’s front three to attack. Unlike Chelsea, Arsenal created and scored from their counter, and conjured more chances through Ozil receiving and creating between lines—his influence on the game growing in the second half.
After Arsenal took the lead, Chelsea’s responded by moving Hazard wide of the three and putting Batshuayi on as striker (in place of Pedro), and replacing Moses with Zappacosta. Neither change had much effect, with Batshuayi unable to keep the ball (Elneny getting ahead of him for the ball on numerous occasions), and Zappacosta not getting many opportunities to take on Monreal, due to Chelsea having far less possession in Arsenal’s final third than in the first half.
Arsenal’s changes, made late in the game, were aimed at adding extra defensive control, with Kolasinac covering the left ahead of Monreal and Ramsey covering the right and leaving Ozil as the striker.
Chelsea had a good first half, with lots of possession, creating opportunities and restricting most of Arsenal’s game with the ball (especially Ozil’s influence). Arsenal’s changes in the second half switched the game in their favour. Two unfortunate goals to concede for Chelsea, but, unlike Arsenal, they were unable to adapt the way they played in order to find solutions during the game.