The 24-year-old Olympic gold medalist straight-up dominated the competition at the US Gymnastics Championships in Texas ... winning first place by an incredible 4.7-point advantage.

Of course, Biles is known to be a trailblazer in the sport ... and lived up to her reputation when she nailed her signature "Biles II" move -- two flips and three twists BACKWARDS -- during her floor routine.

FYI -- The move was named after Biles in 2019 ... after she became the first woman to successfully nail it in competition.

Biles explained her decision to go so hard after winning the competition, saying, "I feel like I did try to enjoy it because it could be one of my last championships that I'll attend."

"But it's also the road to Tokyo, and after this we have trials, so we just have to really embrace the moment."

To make things even better, Biles' NFL player boyfriend, Jonathan Owens, was able to watch her in person ... and raved about his girl in a super mushy Instagram post.

"What an amazing experience 👏🏽," the Houston Texans safety said Sunday.

"First time getting to watch you compete in person and you didn’t disappoint. It’s so cool that i get to watch you do what you love, and be the best at that ‼️ I’m so proud of you my lil champ 🥰❤️."

"Trials up next and you already know I’m there!! Love you baby."

Biles responded to the touching shoutout ... saying, "I love you so much 🤎 I’m so happy you got to come watch while in the middle of OTA’s 😘😘 you a real one."