The fifth stage covered almost 114 miles of mostly flat terrain from Chambord to Montargis.
Armstrong retained the yellow jersey with an overall lead of 55 seconds after winning Tuesday's team time trial. Armstrong's Discovery teammate George Hincapie, another American, is in second. Germany's Jens Voight was third and American Bobby Julich fourth overall.
McEwen edged Tom Boonen of Belgium for the fifth stage win, his first on this year's tour. Boonen had won two sprint stages in this year's tour.
Racers face a mostly flat 124-mile ride from Troyes to Nancy in Thursday's sixth stage of the Tour de France.
Notable deaths of 2014 [PHOTOS]
Julius Randle breaks leg during NBA debut