For one team, it's all about pride.
Juventus would have to completely stop playing in order for Napoli to catch them and qualification for the Champions League is all but a certainty for Edinson Cavani and co.
For the other, it's about European competition. If Inter Milan didn't already view this season as a disaster, failing to qualify for European competition would be the final straw.
Regardless of your views of Inter, the key in this match is quite simple: be responsible on defense. Beating Napoli is a whole lot easier if you don't make it too easy for them to score.
Napoli's been lethal in their last six games. They have 17 goals in that stretch.
Yes, you read that right, 17 goals in six games.
In that same stretch, Inter Milan have allowed 10 goals. They lost four of those six games.
That's the key to Sunday's game.
If Inter try to play a wide open game, if they try to force offense, Napoli's counter attack will punish them. On the other hand, if Inter are disciplined and patient, they might be able to frustrate the Partenopei and leave the San Paolo victorious.
Napoli have been far too lethal lately to get into a shootout with them. Just ask Torino how that worked out for them.
When these two clubs faced off earlier this season, Inter won 2-1. Inter can still attain European qualification, the distance between them and qualification in the league table is miniscule.
Their remaining games after Napoli are against Lazio, Genoa, and Udinese. Not exactly an easy road for the Nerazzurri, but those games against Lazio and Udinese are at home. So they still have a legitimate chance of cracking the top five.
But if that wasn't enough, also adding to Inter Milan's steep climb: Injuries.
The most recent victim was Javier Zanetti. Other injuries include: Diego Milito, Rodrigo Palacio, Antonio Cassano, Esteban Cambiasso, Yuto Nagatomo, Dejan Stankovic, Walter Gargano, Fredy Guarin, Walter Samuel, Gaby Mudingayi, Joel Obi, Ibrahima Mbaye, and Luca Castellazzi.
With the above in mind, it would take a small miracle for Inter to beat Napoli at the Stadio San Paolo.