Napoli condemned last season's Champions League runners-up Borussia Dortmund to their first defeat of the season on Wednesday as the Germans' European campaign endured a disastrous start.
Gonzalo Higuain and Lorenzo Insigne grabbed the goals in the Italians' 2-1 Group F win after Dortmund had goalkeeper Roman Weidenfeller red-carded on the stroke of half-time, with coach Jurgen Klopp also sent to the stands.
"All things considered, it was a deserved defeat. Napoli passed the ball well and we tried everything we could," said Dortmund midfielder Nuri Sahin.
"Every defeat hurts, especially when you know that a win would have been huge for our campaign.
"Napoli are a quality side and when you are down one man, it is very difficult."
Napoli soaked up early pressure from the Germans who went into the match with a perfect record of five wins in the Bundesliga and not having lost a match since their Champions League final defeat to Bayern Munich in May.
Marco Reus slid a fine pass through for Robert Lewandowski in the 26th minute, but the Polish striker's left-foot shot was well-saved by Pepe Reina.
Sven Bender then saw his volley from the edge of the box take a deflection over the crossbar.
Napoli grabbed the lead on the half-hour mark.
Camilo Zuniga crossed from the left for Higuain to get in front of Marcel Schmelzer and head the ball into the bottom corner beyond the dive of Weidenfeller.
It was the Argentine striker's second goal in successive games at the Stadio San Paolo, after netting in the weekend win over Atalanta, and his third in three games.
Klopp was so incensed by the goal that he was sent to the stands for his protests.
Ten minutes before the break, Reus volleyed wide of the target before the night got even worse for last season's runners-up.
Captain and goalkeeper Weidenfeller came rushing off his line to deny Higuain but was sent-off for handling outside the area.
Australian goalkeeper Mitchell Langerak came on to replace Weidenfeller and he was straight into action having to stop Higuain's low free-kick.
Langerak denied Gokhan Inler on the hour mark before Reus missed another golden chance when he shot over the bar.
Dortmund were made to pay for their wastefulness.
In the 67th minute, Insigne found the target when he curled a free-kick around the Dortmund wall and in off the underside of the crossbar.
Three minutes from time, Zuniga volleyed the ball into his own goal off the far post to give Dortmund hope but it was too little, too late.