The Naples club, who won their only two Italian titles in 1987 and 1990 thanks to the magic of Diego Maradona, could have profited from Milan's 0-0 draw with Lazio on Tuesday but were instead deservedly beaten in Verona.
Davide Moscardelli opened the scoring with a superb turn and shot in the first half and Gennaro Sardo broke into the box to make it 2-0 early in the second period.
Serie A's leading scorer Edinson Cavani, who bagged another hat-trick in Sunday's 4-0 win over Sampdoria, was kept quiet by Chievo's defence as Napoli showed stage fright yet again when it mattered to dampen fans' hopes of a shock scudetto.
The once mighty Juventus sank further into the mire and further away from a Champions League spot following a 2-1 defeat at Palermo, the fourth time in a row they have failed to win in all competitions.
Striker Alessandro Matri made his Juve debut having joined on loan from Cagliari on Monday but the Turin side, seventh last term, allowed Palermo to leapfrog them and now lie eighth with just 15 games left this season to spare their immense blushes.
GOALSHY SAMPDORIA
Under pressure Juve coach Luigi Del Neri, who arrived from Samp at the start of the season, was upset by the referee.
"There were fouls not given and the penalty not awarded was shocking. They are taking us for a ride," he told Sky television.
Fourth-placed AS Roma suffered a disappointing 1-1 home draw with second-bottom Brescia and Udinese's storming run came to an end with the same scoreline against plucky Bologna.
Fiorentina again left out Adrian Mutu despite his apology for walking out of training and leapt up the table with a 1-0 victory over Genoa.
Fellow mid-table side Sampdoria, having let main strikers Antonio Cassano and Giampaolo Pazzini leave in January, again looked utterly goal-shy in a 1-0 home loss to Cagliari.
At the bottom, Ernesto Chevanton's stoppage-time goal gave Lecce a 1-0 win at Parma while Cesena and Catania drew 1-1.
Champions Inter Milan, 10 behind Milan in fifth and with another game in hand, visit basement side Bari on Thursday with Wesley Sneijder back in the squad after injury.
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