It was a month-long gamble that could have ended up on the dressing room floor, or at least in the back of the closet. Instead, a gutsy move has catapulted a relatively unknown clothing designer onto dozens of websites—and yes, sales are also on the up.

Sydney, Australia-based designer Johanna Johnson spent a month making a one-of-a-kind Emmys dress for Mad Men star Christina Hendricks. The actress hadn't requested it, and there was no guarantee she would wear it. (Actresses sometimes don't even wear the dresses they actually request, changing their mind at the last minute.)

Johnson, who's been making lavishly beaded 1930s-inspired pieces for five years, already knew Hendricks liked her style: The actress wore a $2,500 glass bead and Swarovski crystal encrusted silk georgette cape to her Superman premiere in New York in February. She'd found the piece through a stylist.

"She loved it so much that she asked after if I minded if she kept it and I said 'of course not, I'd love you to have it,'" Johnson, 36, tells Later in Lucky magazine, Hendricks listed it as her number one favorite thing, "even above the earrings her husband bought her for their wedding," Johnson notes.

So Johnson, who started her bridal and couture business five years ago when she couldn't find the wedding dress of her dreams, decided to create a custom hand-beaded silk gown for Hendricks and present it to the actress as a gift. She spent weeks researching the silhouettes that suited Hendricks best and thinking about the beading patterns. (Read more on how to break into the fashion industry.)

"I wanted to create the ultimate gown," Johnson says. She tried not to think about whether or not Hendricks would actually wear it. "I tried to stay positive," she adds. Then she and her team spent about a month actually crafting the gown. The company has 20 employees, up from just five last year, in a 200-year-old historic building in Sydney.

Two weeks ago, Johnson got word Hendricks planned to wear her design and had chosen hair and makeup to match it. (She also felt pleased that the gown fit Hendricks so well it didn't even require a final fitting in Los Angeles.)

"But until it's on their backs I don't believe it," she says. However, the company did redesign its online store just in case. They launched it the weekend before the Emmys. "We'd hoped to launch it a week earlier to work out any glitches, but it didn't happen," Johnson says. (Learn how to design an e-commerce page.)

Hendricks wore the gown and landed on People magazine's Emmys best dressed list. On the red carpet, the Mad Men star called the dress "extraordinary." She added: "I thought it was so beautiful, it was the only one I tried on.''

Within minutes, the company recorded its first online sale. The site temporarily crashed from the traffic Monday morning, and social media was up by 300 percent. Sales in the first 24 hours after Hendricks appeared wearing the dress were "double the usual sales," Johnson said. Sales for Tuesday (Sydney is 10 hours ahead of EST) havn't yet been calculated, but "they're up significantly," she says. She's been so busy since the dress went live that she hasn't had time yet to celebrate. "Maybe on Friday!" she says with a laugh.

Johnson thinks the red carpet is key to brand-building: "It's crucial. It's really important. The red carpet side of things allows us to showcase what our brand does. And for us to be able to stand up to old-world couture houses and compete on an international scale is just incredible."

Previously, Johnson dressed Maria Menounos and Cheryl Hines for the Oscars and Julia Ormond for the SAG awards. "That was dipping our toe in the water," she says.

Her next challenge: Keeping the quality while expanding. "We don't want to grow too big too quick," Johnson said. "We want to hand finish everything in Australia." (Get tips on how to keep up with a fast-growing company.)

What's the biggest gamble you've taken? Did it pay off?