And Francisco Costa turned out an almost all-white collection that showed he is finally comfortable in his role after two years as Calvin Klein's head designer.
The audience included Claire Danes and Sean Diddy Combs, a financial backer in Posen's company.
"Zac's clothes are pretty, fun, fresh and cheeky. They're supposed to be," said Lesley Jane Seymour, editor in chief of Marie Claire. "He has a sense of whimsy that I think is lovely."
Posen showed some realistic looks, including a flirty green and gold dress and a chic lavender cutaway trench. A gray houndstooth blouse and shorts made a somewhat convincing case that shorts could be part of an evening ensemble.
Wang's collection blended the romanticism of the French painter Henri Matisse with the gutsiness of America's Wild West. The result was a collection with beautiful construction and intricate details.
An iridescent beaded skirt in dark green taffeta, a black lace bed jacket and a funky black taffeta eyelet blouse were among the most noteworthy garments. She also showed a lavender silk corset jacket and a navy floral brocade peasant skirt.
"In the dream world of Matisse and the gritty reality of the American frontier, the diversity of women in our society offers the chance for greater exploration and even greater inspiration," Wang said in her notes.
Wang, who is best known for her red carpet dresses, pushed the boundaries there, too. A star willing to break away from the traditional satin gowns for Wang's black tulle empire waist shift surely would be applauded.
The Calvin Klein collection -- another favorite of the stars -- earned a fan in Marie Claire's Seymour.
"It was well executed and different. It had its own look -- he wasn't trying to be the old Calvin Klein -- but it also was minimal and sexy just like the best Calvin Klein collections are."
The clothes featured plenty of volume: dresses made of layers of sheer cotton voile, swinging trapeze coats and a layered silk tulle skirt.
There were a few splashes of color, including a purple silk chiffon dress. Other standout dresses with a lot of easy movement were an apron dress with a hemline of stitched circles and a pleated jersey dress with an empire waist.
Fashion Week ends Friday night with the runway debut of Gwen Stefani's L.A.M.B. line and "Fashion for Relief," a celebrity runway show to raise money for victims of Hurricane Katrina.