How many of us have been in the stands at a college football game, part of a giddy fan base in face paint, sweatshirts and hats awash in team colors?

If only we had noticed what Sterling Wilson did that fateful fall 2011 day at the University of Southern California.

"No one had USC sunglasses," Wilson recalled.

That simple observation has vaulted him and high school friend Erin Reilly to impressive heights as the founders of Pop! Promos, a profitable business with 1,660 percent revenue growth from 2012 to 2014, earning it the title of the Philadelphia region's fastest-growing private company in October.

"Our plan is to grow and grow quickly," said Reilly, CEO of Pop! Promos. Although she and Wilson, both 26 and residents of Old City, would not disclose their company's revenues, Reilly indicated they are significant.

Surprisingly so.

"There was no way I thought we would be where we are now," she said. "I was not expecting to build a multimillion-dollar company."

Wilson was. He's the numbers guy in this business partnership and president of Pop! Promos.

"I'm just frustrated it took so long," he said with a smirk, seated earlier this month inside the drafty shell of a former gym in Northern Liberties that was under renovation. Pop! Promos moves in Monday.

Its 17 employees (three more will join in February) - now crammed into 2,000 square feet on Fourth Street in South Philadelphia - will soon occupy three times that space. The company also has three employees in China, where all manufacturing is done, and four in India, where many of the virtual renderings and proofs for orders are designed.

Pop! Promos' product line has grown, too, to 17 items in all, including woven beanies, lanyards, knit gloves with touchscreen sensors, iPhone chargers, and sticky wallets. The expansion has been in response to requests from clients, the majority of whom are no longer the schools themselves, but, rather, promotional-product distributors whose customers are many of the Fortune 500 companies, Wilson and Reilly said.

What makes Pop! Promos unique, they said, is making high-quality products from scratch, to precise color and other custom specifications.

The order for that first batch of USC sunglasses more than four years ago was placed by Wilson just after he returned to the school for his senior year, following a one-year leave of absence spent in China working for a pharmaceuticals manufacturer.

The day after the football game, Wilson, with the help of contacts in China, placed an order for 2,000 pairs of sunglasses in USC colors. When they arrived, he pedaled around campus on a bicycle with a sign in red Sharpie that read: Game Day Sunglasses $10. He sold out in three days.

Four months later, Wilson and Reilly met in Delaware to incorporate the company then called College Glasses. Reilly was attending Johns Hopkins at the time, majoring in international studies; Wilson, studying business at USC, was in Philadelphia to compete in a national squash tournament.

Impressed that weekend by a proliferation of "young people" and "great restaurants," reasonable rent and "construction everywhere," Wilson said they decided to locate their new company in Philadelphia - largely foreign territory to both of them. She grew up in Somers, N.Y.; he in Cicero, Ind. (They met at the Kent School, a private college-preparatory school in Connecticut.)

They changed the name of the company to Pop! Promos in 2012, when their offerings expanded well beyond college-theme sunglasses.

Future success will depend, in part, on "continuing to know how to vet next opportunities so they're building on their strengths," said Margaret Berger Bradley, executive director of the 10,000 Small Businesses education program taught at Community College of Philadelphia and funded by Goldman Sachs.

Reilly participated in the program in 2014, impressing more experienced classmates, Bradley said.

"She's just so operationally savvy for her age."