Celtic exacted revenge on St Mirren at Hampden by trashing them 6-2 to reach the Scottish Cup final.
But it wasn't all plain sailing - with Martin O'Neill's men needing extra time to set up a May 23 showdown with Neil Lennon's Dunfermline.
They broke the deadlock inside the opening minute when Buddies keeper Ryan Mullen was caught on the ball and Daizen Maeda closed him down to force the ball into the back of the net.
Hoops' struggled to build on their dominance for much of the half but on the stroke of the whistle doubled their lead when Anthony Ralston rattled one past 17-year-old debutant stopper Grant Tamosevicius, who had to replace the injured Mullen.
Craig McLeish's St Mirren needed the third goal to keep them in the tie and did so eight minutes into the second half when Mikael Mandron beat Viljami Sinisalo with a fantastic header.
Despite a raft of changes, Celtic's energy levels wained and a stunning finale saw St Mirren force extra time. Sub Jake Young flicked a ball over the top and Mandron held off Auston Trusty to lash a strike into the far corner for his second of the game.
With the Hoops looking shakey, Saints fan would have been hopeful of their side striking a killer-blow in the extra 30 minutes to keep them on course for a cup double.
But as it turned out, the complete opposite happened, with a rejuvenated Celtic netting four goals in 12 minutes to get revenge for their Premier Sports Cup final loss to the Paisley team back in December.
Sub Kelechi Iheanacho helped himself to a quickfire brace, with fellow replacement Luke McCowan also getting in on the act.
And it was top goalscorer Benjamin Nygren who rounded off the scoring to give the St Mirren contigent inside Hampden even more agony.
