Hours earlier, Beggs pinned Kailyn Clay to improve to 56-0.
"It's really exciting to have this much media attention on our wrestling event because of the greatness that's here and those 768 students. It's a shame that 767 of them aren't getting much attention" said UIL deputy director Jamey Harrison.
Beggs is a junior from Euless Trinity in the Dallas-Fort Worth area. His family has said he would rather be wrestling boys. Some girls and their advocates agree.
They say the testosterone Beggs has been taking while transitioning from female to male has made him too strong to wrestle fairly against girls. But state policy calls for students to wrestle against the gender listed on their birth certificates. So Beggs beat Taylor Latham and Mya Engert handily on Friday.
In the semifinals, the match was halted for a couple of minutes because Beggs had a bloody nose. Trainers finally managed to stop the bleeding and the fight resumed. Not long after, Beggs slammed Clay on the mat and pinned her.
A 17-year-old transgender boy won a Texas state girls wrestling title and took to Facebook Sunday, reacting to the controversy, saying, in part, "We looked all the haters in the face and said, 'We just want to wrestle,' and that's what we did!"
Mack Beggs won Saturday afternoon's championship match 12-1 over Chelsea Sanchez of Morton Ranch High School.
He and Clay shared a long hug before an official raised Beggs' arm to signal victory, and the wrestler scurried off the mat. Clay's coached shouted to reporters that she "did not have permission" to talk to them after her loss and both of her parents declined comment.
Beggs, who reached the state tournament after two opponents forfeited, will face Chelsea Sanchez for a shot at a state title.
Beggs' participation comes at a crucial moment, with the public and politicians debating the growing belief that gender is fluid. Just this week, the Trump administration announced an end to federal protections that allowed transgender students to use facilities based on their gender identity, leaving states and school districts to determine their own policies.
And in Texas, lawmakers are considering a bill similar to HB2, the North Carolina law that prompted the NBA to move this year's All-Star Game out of that state. If passed, the Texas version, called SB6, would require transgender people to use the bathroom of their "biological sex."
The University Interscholastic League, which oversees athletics in Texas public schools, enacted the birth certificate policy Aug. 1.
Attorney Jim Baudhuin tried and failed to get injunctions before both the district and regional meets to prevent Beggs from competing while he transitions. He told The Associated Press earlier this week he doesn't blame Beggs for the situation, but faults the UIL.
"The more I learn about this, the more I realize that she's just trying to live her life and her family is, too," Baudhuin said. "She's being forced into that position. Who knows, through discovery we may find out that's not the case. But every indication is, the way the winds are going now, the blame rests with the UIL and the superintendents."
Despite criticism of the policy, UIL executives don't envision a change.
"Ninety-five percent of the school superintendents in Texas voted for the rule as it was proposed, which was to use birth certificates," Harrison said. "So any rule can be reconsidered, but ... given the overwhelming support for that rule, I don't expect it to change anytime soon."