Gary Hooper fired home from close range after 23 minutes following a double mistake by United defender Garry Kenneth.
Kayal made it two shortly after half time when he fired in with his weaker left foot to put the game beyond utd.
Celtic left it late to add anymore goals as the third came with five to go when Kris Commons drove another home.
There was time for united to grab a goal in injury time when Russel got a consolation goal.
Daryl Murphey cancelled that goal out 2 minutes later when he held off united defenders before chipping the ball past Pernis.
Sorry for late update guys,Been ill all day.