Both women were fighting without headgear for the first time but it didn't seem to be a factor as they traded punches freely before a sparse but appreciative crowd. Shields won all four rounds on the scorecards of the three ringside judges.

Shields, who became the first American woman to win a gold medal in the 2012 Olympics and added another in Rio in August, had vowed to be impressive in her first pro fight. And she wasn't shy about trading punches with Franchon, a Baltimore fighter who lost to her during the Olympic trials in 2012.

Shields was pushed to the canvas twice by Crews, who started strong but seemed to tire quickly.

"It feels so good to have just made my pro debut," she said. "This is what I've been training for. I'm faster and I hit harder."

Shields, from Flint, Michigan, weighed 167 pounds to 168 for Crews.

The 21-year-old Shields said she plans to fight up to 10 times in her first year as a pro. Her goal is to one day headline a pay-per-view card of her own.

"I believe 150 percent in my boxing ability," she said before the fight. "I know I'm a great fighter. I fight better than 90 percent of the men who box now. I just know that, and I'm not at my best yet."

Women's boxing has largely been a fringe sport in recent years, and women have rarely appeared on televised cards. While the fight was on the undercard of Kovalev-Ward, it wasn't a part of the pay-per-view telecast.