Carlo Ancelotti's much-changed Napoli kept the pace on leaders Juventus thanks to a stoppage time free-kick from Arkadiusz Milik.
Having left out the likes of star men Marek Hamsik, Lorenzo Insigne and Dries Mertens, the Polish striker fired in the winner in a largely frustrating encounter dominated by the away side.
In an even first half, Adam Ounas's effort was comfortably saved by home keeper Alessio Cragno, before both Diego Farias and Paolo Farago were denied by David Ospina.
Napoli stepped up the tempo in the second-half and could have had three or four if it wasn't for their wasteful finishing, as Piotr Zeilinski and Milik were found guilty.
Knowing only a win would continue their valiant attempt to catch leaders Juventus, Ancelotti threw on both Insigne and Mertens, but it was Milik's contribution that would prove pivotal to spare his side's blushes.
Key Talking Point
With former Liverpool man Ragnar Klavan and his partner Filippo Romagna proving a stern force, the Rossoblu certainly matched their opponents defensively.
Ultimately though, neither could prevent Milik's stunner and with just three wins all season, Rolando Maran's side will be nervously looking over their shoulder in upcoming weeks.
Starting XI: Cragno (6), Pisacane (5), Romagna (6), Klavan (6), Padoin (5), Ionita (6), Bradaric (6), Farago (6), Barella (6), Farias (7), Pedro (6).
Substitutes: Sau (5), Andreolli (6), Cigarini (N/A)
Whilst defensively solid throughout, it was Cagliari's attacking duo Diego Farias and Joao Pedro who caused problems - particularly the latter.
Their best opportunities both fell to Farias, whose goal-bound effort was denied at blank-range by keeper David Ospina, before blazing his header over in the second half.
Had the home side taken one of a few chances, it could quite have quite easily been a different outcome.
Simone Padoin faced a torrid evening against opposite number Ounas. The 34-year-old veteran was often overrunn by the speedy Algerian. In fairness, his midfield teammates didn't offer Padoin much protection.
Key Talking Point
After seeing rivals Juventus extend their lead to nine points on Saturday, Ancelotti's men couldn't afford to slip up against a side winless in their previous five league games.
The decision to exclude several regulars looked to have backfired, often finding a Cagliari defence in stubborn mood in front of their home faithful. On the contrary, Ancelotti would have been pleased with his side's attacking display and endeavour that was rewarded in the end.
Starting XI: Ospina (7), Malcuit (7), Maksimovic (7), Koulibaly (7), Ghoulam (6), Ounas (8*), Allan (6), Diawara (6), Zielinski (7), Fabian (7), Milik (7).
Substitutes: Mertens (6), Insigne (5), Callejon (5).
Despite facing an inspired Cagliari outfit, it was the Gil Azzuri's young winger Ounas who impressed throughout. He was at forefront Napoli's typically intricate attacking play and came close in the opening stages, forcing home keeper Alessio Cragno in to a smart stop.
The 22-year-old was eventually replaced by Insigne, but not before giving Ancelotti a selection headache ahead of their upcoming fixture schedule.
Cutting a frustrated figure, midfielder Amadou Diawara didn't enjoy the best of performances. Given a rare start, the Guinean international was found guilty of several misplaced passes - with his fellow midfield counterparts Piotr Zeilinski and Fabian Ruiz proving more effective.
Ancelotti's men host SPAL next Saturday, before a crucial second vs third clash with Inter that could see Napoli steer nine points ahead of their rivals. Meanwhile, Cagliari face a daunting task away at Lazio on matchday 17.