Inter gave their Champions League hopes a big boost while simultaneously striking a potentially fatal blow to Napoli's Serie A title chances with a 2-0 victory at San Siro on Saturday.
Roberto Mancini's Inter went into the contest against the title hopefuls six points adrift of third-placed Roma and looking to crank up the pressure on the capital city club, who play Atalanta on Sunday.
Second-placed Napoli's need for the points was equally crucial as a win would have seen them move to within three points of Juve ahead of the league leaders' encounter with Palermo.
But the visitors lacked penetration in the absence of suspended top scorer Gonzalo Higuain, and first-half goals from Mauro Icardi and Marcelo Brozovic earned a deserved win for Inter.
In-form Nerazzurri captain Icardi got the hosts off to a great start with his fourth goal in five matches after just four minutes, despite suspicions of offside, and he then turned provider for Brozovic to strike on the counter-attack, making it 2-0 before half-time.
Napoli - who won November's reverse fixture 2-1 - continued to toil in the final third after the break, and Jeison Murillo wasted a fine chance to add further gloss.
The match marked the first meeting between Inter boss Mancini and Maurizio Sarri since the Napoli coach was banned for directing a homophobic slur at his counterpart during a Coppa Italia tie in January.
There was a handshake between the rival coaches pre-kick off, though, and Mancini was celebrating first in the fourth minute.
Gary Medel's excellent ball over the top was brilliantly controlled by Icardi and the skipper provided a clinical left-foot finish, Napoli's pleas for offside going unheard.
Napoli dominated the ball but were restricted to long-range efforts. Marek Hamsik's dipping shot was safely parried by Samir Handanovic before the Inter goalkeeper made a brilliant one-handed stop from Allan's drive.
Inter had scarcely threatened since the goal, but Napoli were let off the hook when Stevan Jovetic's teasing right-wing cross was headed wide at the back post by Ivan Perisic with the goal gaping.
It was 2-0 before the break. Jovetic's throughball picked out Icardi and he brilliantly teed up Brozovic to dink a fine finish past Pepe Reina.
Napoli still struggled to penetrate after the break, but Jose Callejon was unlucky with a well-controlled volley from Hamsik's cross that cleared the left-hand post.
Inter were keen to exploit the counter-attack and Murillo wastefully headed over the crossbar when unmarked from Icardi's corner.
Soon after, Reina spilled a simple ball into the box and Kalidou Koulibaly headed Jovetic's chip off the line.
The visitors tried to commit men forward in the closing stages, but Inter - who had failed to beat Napoli in their past six league meetings - controlled the game brilliantly and held firm for a crucial win.