WBO light-heavyweight champion Cleverly has been matched against the little-known American for his homecoming fight.
While the unbeaten 24-year-old from Cefn Fforest hopes to treat the expected sell-out 5,000 crowd to a fine spectacle, he has ruled out complacency creeping into his preparations.
"It would be absolutely stupid and naive to underestimate any opponent in boxing, especially in a world title fight," he said.
"It would be recipe for disaster. A lot of people have written Tommy off, but they're not the ones who are stepping into the ring.
"When you face another trained fighter, you must be on your game, especially at this level.
"I've prepared even better than I have for any other fight.
"Tommy's got nothing to lose and can give it everything knowing there's a big prize at the end of the line.
"It's my ambition to remain unbeaten and prevent that from happening.
"I want to enjoy the performance and put on a good display of boxing.
"It could go the distance and the most important thing is that physically and mentally I'm prepared to go 12 rounds."
The unheralded Karpency has lost two of his 24 fights and had most people scratching their heads when he was unveiled as Cleverly's next opponent.
But the 26-year-old from Pennsylvania insists he is capable of causing a major upset.
"I'm not sure who Nathan was in negotiations with for this fight, but for me this is the pinnacle of the sport, a world championship bout," he said.
"The reason I was chosen as an opponent doesn't affect my drive to win whatsoever.
"I've gone through my whole career without a promoter, my father's my trainer and manager.
"I've been written off and that doesn't really bother me, but I imagine Nathan's camp haven't written me off.
"I believe I can beat any light-heavyweight in the world. If I didn't, I shouldn't be in sport."