A strike of real quality 10 minutes into the second half proved enough to return Europa League-chasing Parma to winning ways following three defeats on the spin.
While their title bid has been over for some time, Napoli retain ambitions of catching second-placed Roma but now trail the capital club by 12 points with only six games remaining.
Ezequiel Schelotto and Jonathan Biabiany combined well to test Jose Reina in the opening minutes but Parma would otherwise struggle to create chances in the first half.
Napoli had the ball in the back of the net after 10 minutes, yet the goal was ruled out as Federico Fernandez was judged to be offside when nodding Lorenzo Insigne's free-kick home.
The Azzurri soon began to take control and, after Felipe made a desperate tackle on Jose Callejon when the Spaniard loped onto Insigne's pass, Gonzalo Higuain clipped just wide from Jorginho's long ball forward.
Gokhan Inler's speculative drive from distance bounced beyond Antonio Mirante's goalmouth on the half-hour mark.
Parma's best chance of the half arrived five minutes before the break as Raffaele Palladino sent the ball across the box to the far post, where Mattia Cassani turned it back inside.
No black-and-white shirt could get a boot in, however, and the match remained goalless at half-time.
A determined Parma side emerged for the second half and within minutes Schelotto had headed over the bar while Biabiany slammed a low drive straight down Reina's throat.
In the 55th minute, Parolo opened the scoring in sensational fashion.
The Italy midfielder grabbed his eighth goal of the season by collecting the ball at the end of a swift counter-attack and rifling it under the bar to leave Reina's head spinning.
Parma's tails were up and, after Afriyie Acquah stormed through the midfield to blast just wide of a post, Schelotto sprung the offside trap to swing an unpredictable low ball through the penalty area.
Napoli had to react and Higuain's last act before he was substituted was to ripple the side-netting with an attempt to convert Jorginho's through-ball.
Rafael Benitez's men grew more desperate as time wore on and Insigne wasted a gilt-edged opportunity when arriving in the box at speed to slam substitute Dries Mertens' cross inches wide of the mark.
The Belgian winger's introduction had an obvious impact on the game and in the final five minutes he teed up both Henrique and Duvan Zapata in good shooting positions, but to no avail.
In the end four minutes of stoppage time were not enough, and Napoli suffered a major setback in their battle to finish as runners-up.