Somdev Devvarman was in three straight NCAA finals, winning the second and third. One of those years he beat Isner in the finals. (I realize, of course, that doesn't eliminate Isner from consideration.) He went 44-1 one year, too.
I'm not knowledgeable enough of college tennis to say those achievements are the bottom line, but they are the most impressive I know of.
I dream of a better world, where chickens can cross roads and not have their motives questioned.