Fabian Ruiz's fine effort earned Napoli a potentially crucial 1-0 victory over Inter in Wednesday's Coppa Italia semifinal first leg.
The Spain midfielder lit up an otherwise turgid San Siro affair with a finish right out of the top drawer shortly before the hour in Milan.
It proved the decisive moment against an Inter side – playing just three days on from beating Milan in the derby – lacking in creativity and Antonio Conte's men will have to show more in a huge Serie A clash with Lazio on Sunday.
Napoli has been well off the pace in the league but Gennaro Gattuso will take heart from a resolute defensive display that sets them up well for the return tie on March 5.
Dries Mertens scooped over from 20 yards during a drab opening, in which Lautaro Martinez should really have done better with a free header from Cristiano Biraghi's floated left-wing cross.
Daniele Padelli made a fine one-on-one stop when Mertens slipped in Giovanni Di Lorenzo, with Napoli's protests that the follow-up was handled by Stefan de Vrij going unheard.
Inter, as in the first half, attempted to play on the front foot without troubling David Ospina early in the second period – aside from a decent header from Romelu Lukaku that the keeper held with ease.
The game needed a flash of brilliance and Fabian delivered in the 57th minute, playing a neat one-two with Di Lorenzo before bending a fine left-footed effort past a despairing Padelli.
An equaliser almost arrived during a mad scramble 15 minutes from time where Lukaku and Christian Eriksen each nearly beat Ospina, who gratefully smothered the ball.
Eriksen and Alexis Sanchez provided some impetus off the bench and fellow substitute Danilo D'Ambrosio almost prodded Lukaku's last-minute flick-on past Ospina but Inter paid the price for a largely toothless display.
What does it mean? Big few weeks for Inter on the horizon
Inter may be leading Serie A but before it plays Napoli again. The Nerazzurri face Lazio, Sampdoria and Juventus in the league and a Europa League last-32 double header with Ludogorets. Chasing this tie at the culmination of that run is not ideal.
Fab by name...
In a game lacking in prolonged quality, it was left to Fabian to steal the headlines with his wonderful goal. It was reward for a disciplined performance in midfield.
'King' Lukaku and Martinez struggle
Lukaku declared "there is a new king in town" after scoring in Inter's derby beating of Milan. There is no denying the impact he has had at Inter but there was little regal about his performance on a frustrating evening. Martinez had a couple of decent opportunities and was also ineffective.
Inter returns to Serie A action with mouth-watering showdown at fellow title challengers Lazio on Sunday, the same day Napoli travel to Cagliari.
-Milan derby took a lot out of us, says beaten Inter boss Conte-
Antonio Conte feels Inter's derby victory over Milan took away a lot of "nervous" energy.
The Nerazzurri fought back to defeat its rivals 4-2 in a barnstorming Serie A encounter on Sunday.
It was a different story on this occasion, though, as Inter struggled to get out of second gear and succumbed to a 1-0 loss thanks to Fabian Ruiz's excellent second-half strike.
Speaking to Rai after the game, head coach Conte said: "The derby took away a lot of energy, especially nervous.
"I made five changes from Sunday to bring in fresh legs, but Napoli beat Juventus, Lazio and Liverpool this season, so that means they've got quality there.
"I'd say that, after Juventus, Napoli have the most impressive squad in Serie A.
"Gennaro Gattuso was smart to sit back, wait and go on the counter. We had the chances and it would've been a fair result if we had played out a draw.
"When you're up against defensive teams like this, you have to move the ball around faster and create spaces.
"We are at the start of this journey, so if some think we are at the same level as a side that was at the top for many years, then I say we're a long way off and have to use these defeats to improve."
Christian Eriksen was again only among the Inter substitutes, with Conte explaining the Denmark playmaker is still finding his best form after being in and out of Tottenham's team.
"He is certainly a player of quality, he needs to rediscover that intensity, seeing as he hasn't played much in the last six months," the ex-Italy boss said of Inter's January arrival.
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