Alegado passed the qualifying heat of the "women's" park and came seventh in the final with a score of 56.96.
She now has her eyes set on reaching the Olympic Games.
"I'm really proud that I got here. My dream is to be a pro skater. I would love to go to the Olympics. I was so excited, you know, because I was able to skate at the Asian Games. It was so fun," she said.
Japan's Hinano Kusaki (15) won the gold medal. Also competing in the final was Lin Yi-fan of Chinese Taipei, who turned 11 years old last month.
Alegado turned nine in March and has her roots in California. She said that she got into skateboarding when she saw her brother doing it while they were at a cousin's house, according to a report in the South China Morning Post (SCMP).
"And I was like, "Can I try? Can I try?" she said. "And I got on the board and just loved it."
Talking about the Hangzhou Asian Games, Alegado said, "I was so excited because I was about to skate the Asian Games — and I just did, so it was so fun!" She said that her brother has now stopped skating. "No, because he was like, "Oh dang, she's better than me now", so he stopped," she said.
In the final, Alegado avoided the wooden spoon, which instead went to Taiwanese 11-year-old Lin Yi-fan. Following her run, she said, "It was really fun, I'm really proud that I got here."
"[My friends at home] think that I'm, like, really cool."
After her performance, the Philippine Olympic Committee tweeted, "Mazel Paris Alegado, our youngest finals qualifier at the #19thAsianGames in Women's Park skateboarding, claimed the 7th spot . WE ARE ALL PROUD OF YOU!!".
The skateboarders in their early-to-mid twenties had some of the lowest scores, including Hong Kong's 26-year-old Lui Yi-ting, who scored 6.36 points in her qualifying heat for women's street.