The striker turned 22 last week and celebrated his birthday in style with a performance full of pace, invention and confidence.
Along with fellow young guns Garry O'Connor, Steven Fletcher and Dean Sheils, Riordan helped Hibs rip through a Kilmarnock side that had won its last four games but had no answer to the home side's pace, guile and energy.
Hibs threatened after just 25 seconds when O'Connor's cross was just cut out by Garry Hay but it was Killie who had the better of the opening exchanges.
Steven Naismith headed into Simon Brown's arms after a Hay free-kick was only half cleared after 10 minutes and a minute later Brown did well to deny Kris Boyd with his legs after Gary Caldwell was dispossessed 25 yards out.
But Hibs survived and Sheils was just inches away from connecting with Riordan's glancing head-flick.
Hibs should have been ahead after 16 minutes when, after Alan Combe saved bravely at Sheils' feet, the ball broke to Riordan and his shoot from the edge of the area was cleared off the line by Hay.
Killie had a great chance after 26 minutes when, from Gary Locke's throw-in and Danny Invincibile's flick, Boyd flicked the ball up and hooked an ambitious effort over his shoulder that Brown just clawed away for a corner.
The pace of Hibs young guns was a constant problem but it was Stephen Glass – at 28 a relative veteran - who played a major role in the opener.
He beat James Fowler to the ball and got to the by-line where his cut back found Riordan just inside the box and the youngster placed a low shot beyond Combe.
And just three minutes later, Riordan and Hibs added a second. Sheils sprung O'Connor whose first time cross was also met first time by Riordan who buried it from 10 yards.
Hibs picked up where they left off in the second half and, after Fletcher shot wide on 50 minutes, Riordan completed his hat-trick in the 53rd minute.
A superb diagonal from Glass picked out Fletcher and, after trying to release O'Connor on the right, instead fired it cross-field for Riordan who chested it down and blasted past Combe for his 15th of the season.
Hibs were running riot and after 63 minutes Glass and Riordan set up Sheils 12 yards out. Combe blocked his shot but only as far as sub Guillaume Beuzelin whose effort was cleared to Caldwell whose dipping drive in turn was tipped over by Combe.
The home side were tearing Killie apart with a series of diagonals letting Hibs behind the Killie defence and O'Connor, Riordan and Sheils all letting fly from distance as Killie struggled to keep things respectable.