Jose Callejon's first-half goal condemned Inter to a sixth consecutive winless game as Napoli earned a 1-0 victory at San Siro on Sunday.
Callejon scored his 11th strike of the league season shortly before half-time but the visitors could have made the result more emphatic had they capitalised on a poor defensive performance by Inter.
Following a nosedive in results, Stefano Pioli's position as head coach of Inter was the subject of intense speculation going into the game and the defeat saw his side miss out on the chance to leapfrog rivals AC Milan into sixth place in Serie A.
Inter now have four games left to save their season, while Napoli's hopes of finishing second and clinching automatic qualification for the Champions League group stages remain very much alive.
After second-placed Roma were beaten 3-1 by Lazio earlier in the day, Napoli's win takes them to within one point of the Giallorossi and the form that has helped them avoid defeat in the league since February is showing no signs of abating.
The play swung from end to end in the opening 10 minutes and the home fans groaned impatiently as Napoli were afforded time on the ball and space to attack.
Mauro Icardi hit the side netting with a header from close range on 11 minutes but Inter then breathed a sigh of relief when Lorenzo Insigne's chip drifted just wide of the target after he robbed Gary Medel of possession.
Callejon flashed the ball across the face of goal after 18 minutes, narrowly missing the outstretched leg of the onrushing Dries Mertens, and Samir Handanovic saved at the feet of the Belgian forward when he broke clear three minutes later.
Marek Hamsik headed just over the crossbar on 25 minutes as the chances continued to flow for Napoli and Insigne went even closer eight minutes later, brushing the outside of the post with a sliced shot after Piotr Zielinski's superb through-ball.
There were just two minutes of the first half remaining when Yuto Nagatomo failed to make a simple clearance, allowing Insigne's cross to find Callejon at the far post and the Spaniard slotted the ball past Handanovic and into the top corner of the net from an acute angle.
Jeison Murillo, wearing a bandage after sustaining a head injury in the first half, inadvertently poked the ball into the path of Insigne after 52 minutes and the Napoli forward curled the ball just wide from 25 yards.
Pioli sent on Ivan Perisic for Joao Mario just before the hour mark, switching to a four-man attack with just two midfielders as they went in search of an equaliser.
Perisic almost immediately broke into the Napoli box and struck a shot that was blocked by the head of Kalidou Koulibaly, and at the other end Handanovic had to be down quickly to push Insigne's low drive around the post.
The Slovenian goalkeeper saved Inter again on 67 minutes when he made a one-handed block to deny Napoli substitute Marko Rog's angled shot from close range, and he made a reflex save with his fingertips from Insigne's back-heel moments later.
Danilo D'Ambrosio picked out Perisic with a deep cross after 70 minutes but the Croat's volleyed attempt went straight into the body of Jose Reina, and Napoli defended in numbers in the closing stages of the game to ensure that was the last clear sight of goal for the home side.
