Marek Hamsik became Napoli's all-time leading scorer with his 116th goal as the Serie A front-runner beat Sampdoria 3-2 on Saturday.
Napoli was behind twice before Hamsik surpassed Argentina great Diego Maradona's tally with the winner shortly before halftime.
Napoli moved four points ahead of second-place Juventus, which hosted fourth-place Roma later.
Inter Milan is five points behind Napoli after Mauro Icardi had a penalty saved in a 1-0 loss at Sassuolo.
Inter had not lost a match before last weekend's defeat to Udinese.
Samdoria got off to a perfect start in Naples as Gaston Ramirez curled a free kick into the top left corner with less than two minutes on the clock.
Napoli leveled in the 16th as Emiliano Viviano could only parry Jose Callejon's volley and Allan fired home the rebound.
Fabio Quagliarella restored Sampdoria's lead in the 27th with a penalty after Elseid Hysaj brought down Ramirez.
It was Quagliarella's first time back at Napoli since he revealed a stalker nightmare forced him to leave his hometown club in 2010.
Lorenzo Insigne was back from injury and he marked his return with a goal in the 33rd, volleying Dries Mertens' chipped pass into the bottom left corner.
Hamsik made history six minutes later.
Allan dribbled through three players in the area before picking out Mertens, who rolled the ball across for Hamsik to tap in from close range.
The only negative note for Napoli was the dismissal of defender Mario Rui 13 minutes from time following a second yellow card.
FREEFALL
Little more than a week ago, Inter was top of the table and the only unbeaten team in the league.
It could find itself fourth at the end of the round after a second successive defeat.
Diego Falcinelli scored the only goal 11 minutes from halftime, heading in a cross from Matteo Politano, who ran almost the entire length of the right flank.
Falcinelli needed several minutes of treatment afterward as he clattered into the post as he scored the goal.
Icardi, who earlier missed a sitter and seen an effort cleared off the line, should have leveled five minutes after the break but Andrea Consigli saved his penalty after Francesco Acerbi's handball.
It was a third successive win for Sassuolo which moved five points clear of the relegation zone.
OTHER MATCHES
AC Milan was booed off the pitch after falling to a second successive defeat, 2-0 at home to Atalanta.
Gennaro Gattuso has just one win from his four league matches since replacing Vincenzo Montella as coach.
Fresh from beating Inter last weekend, Udinese continued its revival by humiliating Hellas Verona 4-0 for its fourth consecutive league win.
Antonin Barak scored twice to take his tally to four goals in the last three rounds. Teammate Kevin Lasagna has four in four.
Lazio beat Crotone by the same result, while Genoa needed a stoppage-time penalty to defeat Benevento 1-0.
Spal and Torino drew 2-2.
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