George Groves came up short in his third attempt to win a world title after a split decision loss to Badou Jack, who retained his WBC super-middleweight crown in Las Vegas.
Groves overcame a first round knockdown at the MGM Grand and fought valiantly in the first half of the bout but his Swedish-born opponent was the superior fighter in the championship rounds.
While the Briton earned the nod on one of the judge's scorecards 114-113, Jack took the other two by scores of 115-112 and 116-111 to hand Groves the third loss of his professional career - following a pair of world title defeats to compatriot Carl Froch.
Groves (now 21-3, with 16KOs) was the favourite heading into the contest, and he hoped victory would lead to a unification bout against IBF champion James DeGale, whom he beat in 2011.
But he made a nightmare start after being unsteadied by a right to the chin towards the end of the opening round and Jack followed up with a swinging shot to the temple which put the challenger on the floor.
He got up straight away and although he was on shaky legs, the 27-year-old made a good comeback in the second by firing off several jabs, with his opponent keeping him honest with some solid counters.
The Londoner was certainly the busier of the two fighters and he ended the fourth round on top with two sharp overhand rights, while he threw 57 punches in the next and seemed to be outworking Jack in the sixth.
But he took a couple of heavy blows in the seventh and Jack was landing the more accurate and eyecatching shots into the eighth.
The 31-year-old, who beat Anthony Dirrell in April to become world champion, focused on softening up the body in the eighth and ninth rounds, and the plan looked to have had the desired effect as Groves seemed to tire.
A piston-like jab appeared to rock Jack in the 10th but the champion recovered and unsettled Groves with a big body shot and then landed another right on the bell.
To his immense credit, Groves continued to be the busier fighter but was coming up second best in the 11th and Jack landed a telling one-two combination in the final three minutes.
While both fighters raised their hands at the conclusion of the bout, it was Jack who was celebrating with a distraught Groves exiting the ring immediately after the score was announced.