The fight had been a chance for the 36-year-old American to avenge his 2008 cruiserweight loss to Adamek, also 36, and move one step closer to challenging world champion Wladimir Klitschko.
But though Cunningham was certain he had done enough for a victory the Pole was the one awarded winning scores of 115-112, 116-112 and 115-113 at the Sands Bethlehem Events Centre.
''I really don't know what more I can do. What can I say? What can I do? Real men cry, real men shed tears,'' said Cunningham, who has now lost three of his last four fights.
''You can't knock everyone out. We did our thing in the ring. It saddens me. I can't be getting cheated like this. It's sad, man, it's sad. It's nonsense. What needs to be done in boxing for this not to happen again? This isn't a game. What else do I have to do?''
Cunningham was effective throughout the bout, using a metronomical jab to control the pace, while Adamek landed the more solid shots.
Stats show Cunningham outpunched his opponent 209-169, and landed 129 of his 349 jabs, while Adamek won out 120-80 in the power-punching stakes.
Unlike his opponent, Adamek was more than satisfied.
"That was like sparring. Not very many punches were thrown. I feel like I can go back into the ring and fight again," said Adamek.
"The fight was close, my trainer told me I had to go after him after the eighth round, and I felt he ran against me. It was part of the plan to come on late in the last 20 seconds of each round. In a few rounds, I tried to attack him, and he would run. He ran. I fought. It's why I won."
Adamek's trainer, Roger Bloodworth, had no problem with the judges’ scores.
"It all depends on what you were looking at," said Bloodworth.
"If you looked at effective punching, which is what the judges saw, they would have give this to Tomasz. If you liked running and being a stylist, then you wanted Cunningham. I think the more effective puncher won this fight, and that was Tomasz."
The result will see Adamek take on Kubrat Pulev in 2013, with the winner scheduled to face Klitschko.