ATLANTA ― Amid intense scrutiny and opposition, University of Pennsylvania swimmer Lia Thomas on Thursday became the first transgender athlete to win a Division I collegiate national championship.

Thomas, a fifth-year senior and transgender woman, propelled past Olympic swimmers to place first in the 500-yard freestyle at the NCAA women’s swimming and diving championships at Georgia Tech.

Thomas finished the race in 4 minutes and 33.24 seconds, about three seconds faster than her season best and a Penn record.

» READ MORE: Photos of Lia Thomas' national championship in the 500-yard freestyle

Emma Weyant, a University of Virginia freshman and U.S. Olympian, placed second with a time of 4:34.99. Erica Sullivan, a University of Texas freshman who’s also an Olympian, placed third with a time of 4:35.92.

“I didn’t have a whole lot of expectation for this meet,” Thomas told ESPN on the pool deck. “I was just happy to be here and race and compete the best I could.”

“I try to ignore it as much as I can,” she said of the opposition she’s faced this year.

“I try to focus on my swimming, what I need to do to get ready for my races, and I just try to block out everything else,” she said. “It means the world to be here, be with two of my best friends and teammates, and be able to compete.”

» READ MORE: Penn swimmer Lia Thomas’ success has prompted national debate about trans athletes. Here’s what to know.

Thomas swam on the Penn’s men’s team for three seasons before coming out as trans mid-2018. She began taking testosterone suppressants and estrogen in May 2019. This is her first year on the women’s team, after last season was canceled by the pandemic.

She holds the nation’s best swim times this year among collegiate women in the 500- and 200-yard freestyle.

Because of her success and identity as a trans woman, Thomas is at the center of a national debate on transgender athletes’ rights to play sports. Thomas’ detractors say that her male-at-birth assignment gives her an unfair biological advantage, while supporters say that because Thomas has followed all NCAA eligibility protocols, she has a right to compete.

Opposition to Thomas was on full display inside the McAuley Aquatic Center on Thursday.

» READ MORE: Lia Thomas just wants to swim. But at the NCAA championships, she won’t be able to stay out of the spotlight.

In the stands, some parents wore stickers that said “Save Women’s Sports,” and two Auburn University parents sported T-shirts with “Women’s Sports Matter.” A number of people in the crowd shook black pom-poms, a symbol of dissent toward Thomas that were handed out by the protesters who gathered outside earlier in the day.

Those protesters, part of a group called Save Women’s Sports (and including Idaho state representative Barbara Ehardt), hung a banner over the railing displaying their organization’s name as Thomas and the other competitors walked onto the deck. At the preliminary races Thursday morning, as the natatorium went quiet and Thomas stood atop the blocks, someone shouted “cheater.”

Some of Thomas’ allies were also in the stands, like Schuyler Bailar, former Harvard University swimmer and the first openly trans person to compete in a Division I men’s sports. A person next to him held up a trans pride flag throughout Thomas’ race.

“It’s a symbol of her resilience. To be able to stand up here and perform as she did, despite all of the hatred, all of the things people have said about her … I think that’s pretty incredible,” Bailar said.

For the trans community, he said, her victory is “another reminder that we can be who we are … we don’t have to dim any of our light.”

The crowd was mostly quiet and still as Thomas briefly spoke with ESPN immediately after her race, one of only three moments she’s spoken with the media this year. She was overcome with emotion, grateful for the opportunity to continue competing.

But when she was awarded atop the medal blocks, some people booed.

In the race, Thomas was neck and neck with Sullivan and Weyant before securing the lead in the final 50 yards.

Sullivan, an Olympic silver medalist in Tokyo, has said that she feels bad for Thomas and the vitriol she has faced this season. She said she would be upset if Thomas beat her this week, but no more upset than if she lost to any other competitor.

Senior Stanford swimmer Brooke Forde, also a silver medalist in Tokyo, placed fourth. Forde was the first to release an on-the-record statement in support of Thomas earlier this season, and on Wednesday, she said she stands by it.

“I’m going to swim my race the way I want to, no matter who I am next to,” she said. “I’m going to be focused on my lane.”

Thomas declined to participate in the NCAA’s mandatory post-win news conference. Penn did not respond to a request for comment.

Thursday afternoon, the about two dozen protesters outside held signs that said, “Support fair sports for women and girls.” The group — whose members traveled from across the country — chanted and passed out brochures and stickers.

The group argued that Thomas’ male-at-birth assignment gave her an unfair advantage — like height, longer limbs, and more strength — compared to other women. They also said Thomas’ participation would be the beginning of the “end of women’s sports.”

Experts have said that trans athletes are underrepresented in sports, and very few ever make it to compete at the elite level. Trans athletes do not transition to get an “edge” in sports, and like all athletes, most are just average, and just want to be accepted and included.

“They are bullying Lia,” Bailar said of the groups.

Some parents and fans cheered and thanked the group as they passed. Tammy and Ben Leehy wore shirts that said “Women’s Sports Matter” in bold orange letters. Their daughter swims for Auburn University.

Many parents who showed support for the protesters declined to be named, saying they did not want to upset their daughters or subject them to social reprisal.

One such mother of a swimmer who competed against Thomas said her frustration was with the NCAA.

“It’s the NCAA rule. It’s not [Thomas’] fault, she’s doing what she’s allowed to do. I don’t think there should be hate against her,” the mother said. “It’s the system.”

About six Georgia Tech students stood outside in support of Thomas with trans pride flags and signs. Ahron Cervania, a Ph.D student, said they wanted to show that protesters who are against Thomas competing are “not representatives of Georgia Tech,” and that the school is “a safe space for trans and queer students and athletes.”

Protesters are expected to stay throughout the week. Thomas will swim the 200-yard freestyle Friday, and 100-yard freestyle Saturday. Two other Penn swimmers, Catherine Buroker and Anna Kalandadze are also present, competing in the 500-yard freestyle and 1,650-yard freestyle.