Ljubicic had 11 wins and 1 loss in 2005, all in live rubbers. He nearly finished the year with a pefect 12-0 record until he lost his second singles match in the final against Hrbaty. He pretty much single handedly helped Croatia beat the USA (with wins against Agassi, the Bryan brothers and Roddick
), Romania and Russia to get to the final that year
McEnroe did have a perfect 12-0 record in 1982, although 3 of his wins came in meaningless dead rubbers that year.
If Berdych wins tomorrow he'll be 11-0 this year with all his wins being live rubbers, will surely be the best out of the lot then, no?