Yes I am confused too. Only early winner of America's Cup beginning with C was Columbia in 1871 but was not the first winner. Were the first two winners not classed as 'yachts' perhaps?
Looking at this again, I am pretty sure the answer must be Columbia. The America's Cup was named AFTER the first winner and so cannot be called the first 'winner' of the trophy. The second 'winner' was an assortment of 16 yachts from the New York Yacht Club. Although one website shows there were two yachts racing for the defenders in 1871, it is highly probable that Columbia is the answer to this mindbender.
The Challenger in the 1870`s race was a boat from Great Britain `Cambria`. Andrew Comstock was the Skipper of the USA yacht Magic in 1870 and Nelson Comstock of the 1871 USA yacht Colombia and Sappho. The original race was in 1851 won by America (USA) Source` Chambers Sports Factfinder`(2005)