Morton held Ladbrokes Championship leaders Rangers to a 2-2 draw at Ibrox on Saturday to move back into the play-off places.
Kenny Miller gave Mark Warburton's men an early lead but an own goal from James Tavernier levelled matters. McCluskey then put Jim Duffy's men in front with eight minutes left but Martyn Waghorn earned Rangers a point.
Hibernian remain three points back in second place after a 1-1 draw with Falkirk at Easter Road. Hibs had John McGinn sent off just before the break and the Bairns looked on course for victory when Lee Miller scored in 84 minutes but Martin Boyle grabbed a stoppage-time equaliser.
St Mirren boss Ian Murray resigned after the 1-0 defeat to his former club Dumbarton, for whom Garry Fleming scored the only goal of the game early in the second half at the Cheaper Insurance Direct Stadium.
Robbie Crawford's second-half goal earned bottom club Alloa a 1-0 win at Livingston as they closed to within three points of Mark Burchill's team.