Claressa Shields took the first step in a long journey by winning her MMA debut

Claressa Shields is a champion. She has showed that for years in the boxing ring, winning gold medals in two Olympics and becoming a three-division world champion (twice undisputed) in an undefeated professional career.

On Thursday night, she showed a different side of her championship mettle by surviving a rough two rounds in her MMA debut before turning the fight her way. She earned a TKO win in the third round of a special showcase featured bout against Brittney Elkin at PFL 4 in Atlantic City, New Jersey.

Shields is not the first professional boxer to win an MMA bout. She's not even the first in her gym, as she trains with the same team in Albuquerque, New Mexico, that is home to Holly Holm, a former boxing champion who went on to win the UFC women's bantamweight championship. But Holm also had a kickboxing background prior to starting MMA. When Shields walked into JacksonWink MMA seven months ago, she was essentially an empty canvas in her new sport.

Shields, the undisputed world boxing champion at junior middleweight and a three-belt champ at middleweight -- and No. 2 in the ESPN women's boxing pound-for-pound rankings -- is 11-0 in that sport and now 1-0 in her new one. To get that win, Shields showed off the fruits of all the training hours she has put in at the gym -- and then defied the coaches who had prepared her.

After being taken down and controlled on the canvas for much of the first two rounds -- but never absorbing significant damage -- Shields finally started landing strong punches early in the third, and she sprawled on the canvas to fend off a takedown attempt. Then, against her coaches' best judgment, Shields elected to keep the fight there on the mat, delivering damage from top position. "Coach kept saying, 'If you get her on the ground, let her up,'" Shields said. "But I'm like, 'I'm not letting her up.' Then she turned towards me, I pushed my hips down again and kept hitting her. And then it was over."

Now, let's not get carried away by this victorious debut. Shields' opponent was a relatively inexperienced fighter who came in with a record of 3-6. Elkin had not competed in MMA in over two years and has not won a bout since 2016. Yet she had her way with Shields for most of the fight, gaining full mount position in each of the first two rounds. But Shields didn't panic. She persevered.

Shields is a work in progress, but her gritty performance showed that she definitely is putting in that work, which sets her apart from some former boxing greats who have tried MMA. Former three-division world boxing champ James Toney, for example, spent all of 18 seconds on his feet and didn't land a single punch on his way to being choked out in 2010 by former UFC champion Randy Couture, who was nearly 50 years old at the time.

Shields, while far from ready to compete with high-level MMA fighters, showed off skills and tenacity that give her something to build upon. There's a lot of building still to come, no doubt. But she's just 26 years old. And she has the heart of a champion.

"Listen, I never doubted myself winning a boxing match in my life. MMA is something like, it's possible I could lose this first fight," Shields said. "I don't want to lose. I'm gonna try dang hard not to lose. And that's what I did. I had a never-quit attitude. ... And when I heard my coaches say, 'Let her up,' I told myself, 'Hell, no.'"