(CNN) -- Inter Milan's lead at the top of Italy's Serie A table was trimmed to seven points on Sunday, after they were beaten 1-0 at Napoli.
Zalayeta (right) celebrates after scoring Napoli's winning goal at home to leaders Inter.
A goal from Uruguayan Marcelo Zalayeta midway through the second half gave the home side their first win under new coach Roberto Donadoni.
According to La Gazzetta dello Sport, Jose Mourinho's side enjoyed the bulk of possession without really threatening their hosts.
Their best chance came after only two minutes, when a powerful header from Walter Samuel was blocked brilliantly by Navarro in the Napoli goal.
The home side were a bigger threat after the break, with Ezequiel Lavezzi in particular catching the eye with his movement.
The impressive Argentine striker set up the only goal of the game after 75 minutes when he drew three defenders towards him before playing in substitute Zalayeta. The striker made no mistake, with a neat right-footed finish.
Napoli could have doubled their lead 11 minutes later, when Julio Cesar tipped over a long-range effort from Manuele Blasi.
To make matters worse for Mourinho's side, city rivals AC Milan moved up to second place in table after a comfortable 3-0 home victory over 10-man Palermo.
The result means Carlo Ancelotti's side are now two points ahead of Juventus, who dropped to third place after a scrappy 2-2 draw at bottom-of-the-table Reggina maintained their poor recent run of form.
Milan took a 10th-minute lead at the San Siro when Kaka scored from the penalty spot after Massimo Ambrosini had been fouled by visiting defender Mattia Cassani.
Ambrosini also had a hand in the second goal 10 minutes later, crossing for veteran striker Filippo Inzaghi to head home his 12th goal of the season from close range.
Palermo were reduced to 10 men when Cesare Bovo was dismissed for a foul on Kaka -- and the Brazilian playmaker scored his second penalty of the game to wrap up the points after he had been fouled by Federico Balzaretti.
Meanwhile, Juventus, who crashed out of the Italian Cup semfinals to Lazio in midweek, were fortunate to come away from Reggina with a point.
The home side went ahead in the 27th minute when Antonio Barilla headed home Daniel Adejo's cross, but Juve levelled before the break when Adejo fouled Vincenzo Iaquinta in the area and Alessandro Del Piero fired home the resulting penalty.
Emil Hallfredsson restored Reggina's lead with a long-range strike but Cristiano Zanetti ensured Juventus grabbed a point.
Fiorentina lie in the fourth and final Champions League place after two goals from Alberto Gilardino helped them defeat rivals Roma 4-1 on Saturday night.
They are a point ahead of Genoa, whose hopes were hit on Sunday after they were beaten 2-0 at Bologna.