Hibs' recent barren spell had coincided with a dry run in front of goal for Riordan, whose 76th-minute free-kick gave his side a vital victory on Saturday.
Substitute Abdessalam Benjelloun earlier missed a penalty as the hosts just about earned their win in what was a war of attrition on a boggy Easter Road pitch.
Kevin Kyle was left out of the Killie squad after playing in a trial match for Russian club Spartak Nalchik in Turkey on Thursday.
Manager Jimmy Calderwood, who revealed yesterday Kyle had flown out for the game without his knowledge, recalled Mehdi Taouil, Frazer Wright, David Fernandez and Jamie Hamill, while Hibs drafted in Alan Gow for the suspended Colin Nish.
Kick-off had been brought forward to 2pm after the demolition of the stadium's East Stand left it without sufficient floodlight coverage.
The missing terrace further exposed the poor quality of the playing surface and neither side was able to enjoy a sustained spell of possession early on.
There was concern for both teams eight minutes in when home defender Sol Bamba and Killie goalkeeper Cameron Bell collided at a free-kick.
Both stayed down for almost a minute but Bell came off worse and was carried off on a stretcher four minutes later to be replaced by debutant Lee Robinson.
The opening quarter was truly dire but Chris Maguire should have given Killie the lead in the 23rd minute when he spun in behind Bamba and lashed against the side-netting.
Riordan then forced the first save of note when his 25-yard curling shot was palmed wide by Robinson.
Seconds later, Gow hobbled off to be replaced by Benjelloun and the casualties continued to mount when Bamba was withdrawn for Paul Hanlon.
The first real moment of quality arrived in the 33rd minute when Benjelloun threaded in Anthony Stokes, whose low finish was brilliantly saved by Robinson.
Inexplicably, the assistant referee awarded a goal-kick, much to Stokes' annoyance.
Makeshift centre-back Manuel Pascali then blocked another Riordan curler before the remainder of the half limped to a conclusion.
The second period began much as the first ended, though Stokes had a sight on goal in the 50th minute when he scuffed a shot wide from 18 yards.
Benjelloun had looked lively since coming on and he won a 59th-minute penalty when Pascali appeared to bundle him over just inside the box.
Benjelloun took the spot-kick himself but it was too close to Robinson, who sprang left to keep it out.
Killie made their second change three minutes later when the fit-again Allan Russell came on for Fernandez.
The home fans were becoming increasingly frustrated as the half wore on.
Some celebrated when Stokes had the ball in the net in the 71st minute but the flag was already up and Robinson made no attempt to save.
Killie immediately withdrew Taouil for James Fowler as they looked like settling for a draw, while Hibs brought on Danny Galbraith for Lewis Stevenson.
Benjelloun mishit a left-foot 20-yarder which Robinson grasped with ease as Hibs' desperation grew.
But their nerves were settled in emphatic fashion by Riordan 14 minutes from time.
James Fowler was booked for bringing down Galbraith 25 yards out and Riordan stepped up to curl a stunning free-kick high past the despairing Robinson.
Killie might have equalised in the 85th minute when Wright sent a free header from Iain Flannigan's corner straight at Graham Stack.
Stokes could have added gloss to Hibs' win in stoppage-time after Liam Miller sent him clear but Robinson thwarted him again, while Maguire volleyed over under pressure in the closing seconds.