Napoli won the first leg with a convincing 3-1 win in Italy. Now, the tie moves to London, where Chelsea will hope to reverse their fortune. With Andre Villas-Boas gone, Chelsea have seemingly gone back to the old guard, but they haven't looked much better.
With English teams failing in European competitions, Chelsea have a lot of outside pressure to play well on Wednesday.
Chelsea are definitely capable of winning, but they need to make up the goal differential, without conceding too many away goals.
Meanwhile, Napoli are looking to knock off another English giant in England. They have put themselves up two goals on aggregate and a decent showing should help them advance.
Chelsea will be playing desperate. If they want to come back, they must play very well. In order to ward off Chelsea's siege, Napoli must play well in a different country.
Here are the tactical keys for each side.