Dec 10 (Reuters) - Norway"s Magnus Carlsen claimed his fifth world chess crown in Dubai on Friday with a crushing 7.5-3.5 victory against Ian Nepomniachtchi, who faded badly after going toe-to-toe with the Norwegian defending champion in the early games. The 31-year-old Carlsen benefited from a blunder by his Russian challenger to win his fourth game of the match, with the black pieces, to take an unassailable lead in the best-of-14 contest. "I didn’t expect it go quite like this. I think it was just a very good professional performance overall. No regrets at all, just very satisfied," said Carlsen. His large margin of victory made it the most one-sided world championship since Jose Raul Capablanca of Cuba defeated German Emmanuel Lasker 9-5 in 1921 - an outcome that few would have bet on during the contest"s initial stages. "After five games there were five draws and I’d had very, very few chances to play for anything more," Carlsen added. "Then everything kind of clicked and after that it all went my way. You don"t expect to necessarily run away with it in a world championship." The contest sprang to life in game 6, won by Carlsen with the white pieces after seven hours 45 minutes and 136 moves - the longest game in world championship history. A dull 41-move draw followed before Carlsen won again with white as Nepomniachtchi, winner of the Candidates tournament in April, blundered a pawn move in the middle game. Nepomniachtchi made another error in game 9, letting his light-square bishop get trapped after just 27 moves and leaving Carlsen on the brink of a fourth successful title defence. After another draw, Friday"s game 11 showed that Nepomniachtchi, the world number five, had not recovered from his earlier defeats as he lost focus again. "These things which happened here, they have never happened to me at basically any events," a disconsolate Nepomniachtchi said of his blunders. "In my career I lost quite some stupid games but not as many in such a (short) time."