A remarkable finish from Josip Ilicic put Gian Piero Gasperini's Rosanero on the road to a first win in eight attempts, a result that would have lifted his side to within one point of safety if not for Cagliari's late rally.
Goalkeeper Stefano Sorrentino, signed from Chievo this week, kept the Rossoblu at bay for 90 minutes but Ribeiro capitalised on one lapse of concentration.
And to add insult to injury, Gasperini and his benched striker Fabrizio Miccoli both saw red for overzealously challenging a marginal call over a throw-in.
It was to be a baptism of fire for Sorrentino as Mauricio Pinilla came steaming into his box inside two minutes, but the veteran keeper stood firm.
Palermo wised up after that early scare and soon took control of the midfield, with Pinilla and Marco Sau forced to feed on scraps for much of the first half.
Victor Ibarbo finally found the ball to unlock the visitors' defence but Pinilla and Sau could not contrive to muster a shot on goal.
Cagliari would pay the price for not taking their chances as Palermo took the lead against the run of play on the half-hour mark.
Andrea Dossena made good progress up the left wing to drift the ball across the box to Ilicic, who unleashed an unstoppable drive beyond Michael Agazzi.
Palermo had Sorrentino to thank for preserving their lead before the interval, though, the 33-year-old making a decisive block when faced with the onrushing Sau.
Cagliari upped the pressure after the break and Gasperini responded by switching to a five-man defence. Substitute Ribeiro tried his luck against the new-look Palermo backline but his final touch left much to be desired.
Sau fared better, though, twisting his body to strike the ball with power, only for the superlative Sorrentino to tip the drive out for a corner.
Time was ticking away and Palermo were headed for a first away win of the season, but Sorrentino was finally beaten on the stroke of full-time.
Danilo Avelar was the man to pick out Ribeiro in a goalscoring position, the Brazilian completing the move with a glancing header.
That sucker-punch was too much to take for Palermo's bench and Gasperini followed Miccoli down the tunnel as a result of some furious exchanges with the referee.
The Sicilians were perhaps lucky to take a solitary point home, though, as Sau missed a chance to complete the comeback by firing wide on the counter-attack.