The Andalusians hauled themselves out of the relegation zone with a late goal which has simultaneously dented their visitors' hopes of qualifying for European competition
Ighalo opened the scoring for the home side shortly before the hour mark only to see Jose Salomon Rondon level matters just over 10 minutes later.
The game appeared to be heading for a draw but Inigo Lopez struck close range with minutes remaining and any hope of Malaga had of turning the game around were ended by the dismissal of Martin Demichelis just moments later.
Malaga had gone into the game knowing that a victory would propel them up to sixth in the standings and they had much the better of the opening period, with Rondon, Santi Cazorla and Demichelis all forcing fine saves out of Granada goalkeeper Julio Cesar.
However, the hosts gradually secured a foothold in the game and took the lead when Ighalo sent a bullet header past Willy Caballero after getting on the end of Mikel Rico's wonderfully inviting cross from the right wing.
Malaga wasted little time drawing level, though, with Rondon tapping home after some neat play by Sebastian Fernandez and Monreal down the left flank.
However, there was to be late drama, with Lopez finishing smartly after Caballero was unable to hold on to Guilherme Siqueira’s strike from distance.
Demichelis then saw red for a reckless challenge on Franco Jara as Malaga slumped to a shock defeat which leaves them eighth in the table while at the same lifting Granada from 18th up to 15th.