Structurally, Chelsea played the 4-2-3-1 that they played against Manchester United, playing Juan Mata in the centre. Malouda was on the wing, but played very narrow. Sturridge started wide to get the ball and in the attacking phase, went inside trying to go past Zuniga. Drogba played in a target man capacity, trying to lay off the passes into the path of Mata, Malouda and Sturridge to run on to.
Chelsea also played a high line during the course of the game, and Napoli's long balls from deep positions constantly troubled them. Gary Cahill and David Luiz were not very effective throughout the game and they were helpless to prevent a Chelsea loss.
Napoli stuck with their usual 3-4-3, with Zuniga and Maggio playing as wing-backs. Zuniga was more conscious of the attacking threat of Sturridge and was generally solid in defense. Maggio was the more offensively conscious of the two, constantly getting forward in attack and linking up with Lavezzi.
The back three were very deep, save Hugo Campagnaro. He was the more attacking of the back three, understandably so because, since only Drogba played up front, there were two men free at the back. Cannavaro was the sweeper, so Campagnaro was the most attacking of the three.
Chelsea seemed slightly aimless in their approach, not really pressing with any energy or effervescence high up the pitch. Napoli, on the other hand, pressed very well and very effectively. However, Chelsea seemed to have a mismatched game plan, in that they played an extremely high line and were also allowing Napoli's deeper players more time on the ball.
Chelsea were also not effective at restricting the Neapolitan counterattacking approach, which was a hallmark of their triumphs against Manchester City. They were often lethargic with the ball, even though they occasionally had some good interplay in between midfielders and defenders. Their game plan seemed to center around playing to Drogba, but he was often isolated or up against too many opponents. He could not get on the ball enough to start attacking moves.
Ezequiel Lavezzi's movement was also interesting in the first half, as he not only drifted into midfield at times into playmaking positions, but also to the other flank, playing as a support to Maggio and Zuniga whenever they came forward.
(Note: dotted arrows show passing direction, and complete arrows show movement)
Napoli were unusually direct, a sign that the coach understood that the best way to counterattack against Chelsea was through the flanks. Chelsea were playing against wing-backs with Sturridge and Malouda and to create a two-versus-one situation on the flanks to get crosses in for Drogba, who needed to get his full-backs forward. However Napoli won the ball so effectively in defence with three center-backs.
Getting Behind Zuniga
This was a key feature of Chelsea's plan of attack: trying to win the ball and break quickly. However, they pressed so ineffectively that the opportunities did not come that often. Malouda on the left was better marked by Campagnaro, who was more advanced positionally. Therefore Sturridge, whose movement and attacking play was more incisive, was Chelsea's best chance of breaking out.
However, Zuniga generally did well defensively. But when he was caught high up the pitch by a Chelsea tackle (preferably when Drogba went into the midfield to help win the ball), Sturridge had space to move into. The first Chelsea goal was cause by Sturridge's movement, with a little help from a defensive mistake from Napoli.
He was the underrated player in the game. Inler was outstanding, indirectly creating two of the three Napoli goals with long passes. He created the second one with a pass to Cavani, who headed in. Inler and Mata were the key midfield players for their respective teams from an tactical point of view, though Mata was largely ineffective in the hole, in part a reflection of of Inler's efforts of marking him.
From a defensive point of view, Inler was the free player when Napoli had the ball because Mata didn't really have a strict man marker and was one of the only Chelsea players with freedom to move around the pitch. That resulted in Inler being a free player when Napoli had the ball.
Till the substitutions, the game was the same as the second half. Napoli's direct counterattacking approach was getting a lot of mileage against Chelsea's high-line approach.
The substitutions changed the game significantly, as Chelsea began to get wider when Lampard and Essien came on for Malouda and Meireles. They moved to something like their normal 4-3-3 that involved Mata moving into the center to make it look like it was almost a 4-1-3-2.
A lack of intensity in Chelsea's approach and a lack of tenacity in midfield, as well as ineptly playing a high line, led to their defeat. Lavezzi and Inler were badly handled as they wreaked havoc with balls from deep.