Froch was previously unbeaten in all 26 of his fights
Nottingham's Carl Froch vowed to win back his world title after suffering the first defeat of his career to Denmark's Mikkel Kessler in Herning.
Froch lost his WBC super-middleweight belt by unanimous decision in the Super Six World Boxing Classic series.
"I'm absolutely gutted that I've lost my title," Froch told BBC Sport.
"But I'm still in the competition and the title is still in the tournament and it's up to me to bounce back from this and win my title back."
All three judges gave Kessler the verdict, scoring the fight 117-111, 115-113, 116-112, a decision that Froch later called a "sham."
The 32-year-old made a bright start to the fight and appeared to floor Kessler in the fifth but it was ruled a slip by the referee.
From then on the Dane came back into the fight and rocked Froch in the eighth before a thrilling climax which saw both fighters stand and trade punches toe to toe.
"I lost my title to a true warrior," admitted Froch. "But I honestly thought from rounds four and five I was wobbling him but what I didn't do was step on the gas and finish the fight.
"I thought I was winning but you've got to be careful when you box away from home and you've got to make sure of the result."
He continued: "I thought I hurt Kessler but when you look at some of the scorecards, I was never going to win that fight.
"It's a bit of a sham and it's upsetting and if it was in Nottingham I would have won that fight. I would have got the decision.
"I took it a little bit of granted, maybe I took my foot of the gas, but I still think I did enough to win the fight."
Having defeated Andre Dirrell in his previous fight, Froch can still qualify for the semi-finals of the tournament if he beats German Arthur Abraham in August.
Kessler also has his sights on a place in the last four after bouncing back from losing the WBA belt to American Andre Ward in his previous contest.
Froch, meanwhile, also revealed afterwards that he had suffered a perforated left ear drum in the lead-up the fight, which affected his balance on the night.
He also admitted to having a "few other niggles" but refused to blame the delay in arriving in Denmark, caused by planes being cancelled following the discharge of volcanic ash in Iceland.
"Fifty per cent of my left ear drum is gone, it's perforated and I went to hospital on Tuesday to have it cleared out. I need to get it checked again," he admitted.
"It affected my balance and I felt a little bit wobbly in there. That was one of a number of injuries I had, but I don't want to make excuses."
His trainer Rob McCraken added: "Every round looked close and Kessler fought the right fight.
"It was close fight he seemed to hurt him but didn't follow those shots up. He needs to be busier in fights, Kessler was badly hurt and he needs to follow up those big shots.
"He had him on the hook a few times and he could have stopped him but he didn't throw the right hand freely enough."