The 29-year-old hit a tame effort towards goal which Algeria goalkeeper Faouzi Chaouchi somehow managed to miss as he gifted Slovenia all three points.
The ball simply bounced through his arms into the back of the net to hand the lead to Slovenia, who managed to close out the encounter, aided and abetted by the fact Algeria had been reduced to 10 men when substitute Abdelkader Ghezzal was dismissed for two bookable offences.
After England and USA drew the opening match in the group on Saturday evening, both sides had a glorious opportunity to defy the critics who suggest they will not qualify for the last 16.
However, this match was a terrible advert for football and an even worse advert for South Africa 2010.
Udinese goalkeeper Samir Handanovic managed to acrobatically punch a Nadir Belhadj free-kick over his crossbar in the opening moments but the game soon plunged downhill.
With little fluidity or deft movement from either side, the match continued to merely amble along with no threats posed by either frontline.
As half-time approached, neither team looked prepared to go forward although after 36 minutes, the game finally got a talking point when Rafik Halliche should have given Algeria the lead.
He had a free header at a corner and although he rose highest, he could not steer his effort on target.
Soon after, Belhadj found Karim Matmour on the right wing but he could not control his shot as he blasted over while, at the other end, Chaouchi superbly tipped a Valter Birsa effort over the crossbar as the game seemed to finally awaken.
After the interval, quality remained thin on the ground as once again neither team had the necessary flair to break the other down.
Andraz Kirm curled one effort goalward for Slovenia that was comfortably saved by Chaouchi but it was all too flat and all too one-dimensional.
Ghezzal nodded over from close range for Algeria with 20 minutes to go and, shortly afterwards, he pointlessly handballed and was rightly dismissed for his second bookable offence.
Algeria's day then got worse as Koren stepped up and hit a speculative effort that Chaouchi missed as Slovenia got a huge slice of good fortune and they now top Group C as a result of this victory.