Ally McCoist's men were aiming for their 15th consecutive league win on the road but Pascali grabbed the only goal late on to take all three points.
Gers striker Nikica Jelavic was inches way from scoring in the opening seconds as he lunged in on Steven Davis' low cross
The home side were then dealt a blow when Danny Buijs pulled up while the Gers' Kyle Lafferty was forced off to be replaced by Kane Hemmings.
The latter tested Cammy Bell with a powerful right-foot shot before Jelavic's looping defensive header came back off his own crossbar.
James Fowler then cleared Sone Aluko's driven shot off the goalline as the game finally came to life while at the other end Allan McGregor somehow foiled Paul Heffernan when he was clean through.
The lively Aluko's shot was deflected onto the post and hacked cleared after a scramble as Rangers pressed but the drama was to come at the other end.
A corner was only partially cleared and Pascali got on the end of Garry Hay's punt forward to flick a header past McGregor.
Substitute Alejandro Bedoya had a golden chance to level but shot straight at Bell and the Killie defence held out for memorable victory.
The result leaves Rangers four points clear of Celtic at the top.
