The ankle injury which saw Steven Fletcher off in the first half took the shine off Saturday’s SPL victory at Easter Road but Riordan benefited by scoring a minute from the break.
Rob Jones doubled the home side’s lead a minute from the end, powering a header over the line from Riordan’s corner.
Hibernian manager Mixu Paatelainen saw no reason to alter his starting line-up after last week’s win voer Celtic.
Hamilton forward Richard Offiong was restored to the first 11 in place of Joel Thomas. Chris Swailes deputised for former Hibs defender Martin Canning, with the player serving a suspension following his red card in last week’s heavy defeat at Rangers.
Hibs, buoyed from their victory over leaders Celtic last weekend, made a bright start and were looking to inflict more damage on a Hamilton team winded by their 7-1 thrashing at Ibrox.
Winger Alan O’Brien was looking to utilise his pace and he managed to make room for a cross from the byline after racing past Swailes but goalkeeper Tomas Cerny was alert to the danger and cut out the pass with Colin Nish lurking at the front post.
Hibs midfielder John Rankin, who left Celtic goalkeeper Artur Boruc red faced when he scored from 40 yards last week, again tried his luck from distance but Cerny got down well to the effort in the 15th minute.
Moments later, Fletcher chipped a cross towards Nish but the striker’s glancing header was easily taken by the goalkeeper.
Hibs were then dealt a blow when Fletcher was forced off with an ankle injury in the 20th minute following a challenge by James McArthur and was replaced by Riordan.
Hamilton created their first chance of the game in the 25th minute when James McCarthy did well to create room for himself 20-yards from goal but his low effort was pushed behind by the goalkeeper.
Hibs passed up a great chance to take the lead in the 27th minute after O’Brien’s corner caused panic in Hamilton’s rearguard.
Sol Bamba rose high at the back post to meet the set piece and his downward header hit the post.
The rebound fell to Nish just yards from goal but the tall striker failed to get his foot around the ball and lashed his shot wide.
Nish then shot from 35 yards with Cerny off his line but his effort just cleared the bar to the relief of the keeper.
Six minutes from half-time, Jones headed David van Zanten’s free-kick goalward but Cerny tipped the ball round for a corner.
However, on a rare attack four minutes later, Hamilton carved open the Hibs defence with Simon Mensing having a clear sight at goal from 10 yards but Yves Ma-Kalambay made a great block.
Hibs finally broke the deadlock 60 seconds before the break. Ian Murray made a lung-bursting run on the counter-attack before squaring for Riordan to tap the ball into the net from close range.
Former Rangers striker Jonatan Johansson, who will join Hibs when the transfer window opens, was paraded before the home supporters at the half-time interval.
When the action got under way in the second half, it was Hamilton marksman Offiong who had the first chance as he cracked a venomous 30-yard shot off the underside of the crossbar with Ma-Kalambay well beaten.
The visitors looked far more threatening and created the next opening too. Derek Lyle just missed the far post with a left-footed strike from the edge of the box.
Hibs were caught napping when Hamilton worked a short corner which led to the unmarked McArthur latching on to a pass inside the box but his effort was deflected wide.
With Hamilton getting bodies forward in a bid to find an equalising goal, the New Douglas Park outfit left large gaps in defence.
Ma-Kalambay had Hibs panicking when he spilt Trent McClenahan’s shot but Bamba was on hand to clear the danger.
Offiong was then booked for a late tackle on Ian Murray as his frustrations got the better of him.
Hibs came close to doubling their lead in the 82nd minute after Jones rose high to meet Hogg’s free-kick but his header came back off the post.
Jones, however, made sure of the points a minute from time when he bulleted a header through Cerny’s hands from Riordan’s corner.