Victory for the hosts would take them to within three points of league leaders Juventus, but a win for the Bianconeri would put them within sight of a second consecutive title.
Midfielder Behrami told Radio Marte: "We know what it means for Napoli. It matters a lot to our fans and to us too. Right now we are second in the league, a very good place to defend.
"From the beginning of this season, we have been proving that we can do even better than that.
We want to fight for something important and we will try to understand if we are able to. On Friday we have the chance to see where we are going.
"In my opinion, this is a key game from the psychological point of view. It can show us who we are and what we can get from this season.
"Juventus is a great team, we will have to attack smartly and at the same time don't let them take any initiative. We must leave a mark, we will try to do it."
Behrami believes the atmosphere at the San Paolo can be a decisive factor and has called on Napoli's fans to play their part.
He said: "Our fans can give us that extra boost, the adrenaline to push us more. They can be our extra weapon to go beyond our limits.
"I ask them to support us, to appreciate what we have been doing in this championship and to consider what we are trying to achieve, that is something very important."
Napoli's pursuit of Juventus has been dented by three straight draws, during which they have scored only once, but the Turin side are well aware of their opponents' talents.
Defender Giorgio Chiellini told Sky Sport Italia: "The match could go either way. It won't be decisive because there is still a long way to go in the championship, but it will of course be important for both teams.
"There have been a lot of games since we met in Serie B and Napoli have improved immensely. They have an ambitious president and, since (head coach Walter) Mazzarri arrived, they've taken a further step up in quality.
"The club has not only become competitive in Italy, but also in Europe, as they showed last year over two legs against Chelsea."
The big games continue on Saturday when fourth-placed AC Milan head to Lazio looking to leapfrog the Romans into third.
Massimiliano Allegri's side are currently two points behind their rivals and must keep their focus on the league before they aim to turn a 2-0 advantage into Champions League victory over Barcelona on March 12.
Vice-president Adriano Galliani told acmilan.com: "We can't think about Barcelona now as we have two games to win first against Lazio and Genoa.
"The next round will be an important one. It's first against second as well as third against fourth. There are many teams going for third - us, Lazio, Inter, Fiorentina, Catania, Roma - six teams for third. It's a league within a league."
Mario Balotelli has already made plenty of headlines since returning to the city last month and this week Inter were fined 50,000 euros after the striker was racially abused by a section of fans.
Balotelli picked up a knock in the derby, which ended in a 1-1 draw, but should be fit for Saturday, although Robinho is out.
Inter, in fifth and a point behind their city rivals, travel to Catania, another of the contenders for a Champions League place, on Sunday while Fiorentina host Chievo.
Eighth-placed Roma will hope to capitalise on teams above them taking points off each other when they host Genoa, Udinese travel to struggling Pescara and mid-table sides Sampdoria and Parma meet each other.
In the weekend's other matches, bottom side Palermo face Torino, Siena host Atalanta and Bologna face Cagliari.