The white, one-shouldered gown, covered in fabric petals and dotted with beads, that she wore to the rounds of balls Tuesday night was by 26-year-old Jason Wu, a rising star in the fashion world but otherwise not well known.
"Her support means so much to designers who can't afford to advertise," said Nicole Phelps, executive editor at Style.com.
The fitted-bodice, gathered-skirt gown was a departure for Obama, who has made a sleek sheath her signature silhouette. She also has shown a fondness for jewel tones. The Isabel Toledo lemongrass-yellow ensemble she wore to the inaugural ceremony and parade was much more what the public has come to expect from Obama.
But the ball gown, worn with red-carpet-worthy dangling diamond earrings by Loree Rodkin, still felt fresh and different.
"It's soft, feminine, but powerful; I wanted to convey all that in a dress," Wu said. "I wanted it to look like a sign of hope."
Hamish Bowles, Vogue magazine's European editor-at-large, who curated the Metropolitan Museum Costume Institute exhibit on Jackie Kennedy in 2001, called the gown "supreme modern elegance. A pitch-perfect choice: appropriately formal but romantic and imaginative."
Clearly President Barack Obama approved. "First of all, how good-looking is my wife?" he asked a cheering crowd just before their first dance at the Neighborhood Ball at Washington's Convention Center.
He wore a single-vent, notch-collar tuxedo with a white bow tie and an American flag pinned to its lapel.
The gown's slight train swirled pleasingly and the new first lady's shoulder-sweeping earrings picked up the gown's sparkle.
It caused a stir on the Web, as devoted fans debated whether it best suited Obama's figure - and their high expectations.
Regardless, the gown will be donated to the Smithsonian, according to tradition, the first lady's spokeswoman said. Surely it will be noted that fellow first ladies Jackie Kennedy and Nancy Reagan also wore white inaugural gowns.
The fashion industry has anxiously looked to the election of Obama for months, embracing his wife as an ambassador, along the lines of Kennedy.
Long loved for her willingness to confidently mix high and mass fashion, Michelle Obama didn't disappoint in accessorizing her day look: green gloves by J. Crew and green patent leather pumps by Jimmy Choo.
"What's so powerful about Michelle Obama is we all see ourselves in her," said red-carpet and magazine stylist Mary Alice Stephenson. "She's a modern woman who is fashionable and even flamboyant in her style and she is still taken seriously."
Toledo, too, said she wanted her outfit to convey optimism.
"I didn't want a traditional blue or red," Toledo said. "That color has sunshine in it. I fell in love with it. So did she."
Whether or not everyone loved the looks, that message clearly came through.
"What I recognized more than anything from our new first lady and Hillary (Rodham Clinton) and everyone else is that everyone was fresh," said fashion designer Kai Milla, wife of Stevie Wonder and an invited guest to the swearing-in ceremony.
