Along with Casar, Efimkin and Mikel Astarloza, he had made a decisive break on the final climb, up the Col d'Agnes, then held off the peloton on a long descent to the finish line and fighting it out for the stage win.
They finally extended their lead when Nacewa finished off a fine move involving D'Arcy, O'Driscoll and Rob Kearney four minutes after the break to claim his first Heineken Cup try.