Bianca Andreescu on how she visualized her win against Serena Williams at the US Open

Bianca Andreescu celebrates with the championship trophy after winning the Womens Singles final against against Serena Williams at the 2019 US Open at the USTA Billie Jean King National Tennis Center, Sept. 7, 2019 in the Queens borough of New York City.PlayElsa/Getty Images
WATCH US Open champ Bianca Andreescu on her big win

The stunning victory Bianca Andreescu scored against Serena Williams at this year's U.S. Open is one the 19-year-old had been visualizing for years.

Andreescu said Monday on "Good Morning America" that she not only pictured herself holding the trophy, but also wrote herself a winner's check from the U.S. Open as far back as 2015 in preparation for the moment that played out at the women's final on Saturday at Arthur Ashe Stadium in Flushing Meadows, New York.

"I’ve been visualizing ever since I was 12 or 13 when my amazing mother introduced me to it," Andreescu said. "I find it very helpful ... I believe we create our reality with our mind."

"For it to actually become a reality is crazy," she said of her first Grand Slam singles win.

Andreescu bested Williams 6-3, 7-5, cutting short the American star's bid to win a record-tying 24th Grand Slam title and her first since giving birth to daughter Olympia two years ago.

Andreescu, who lost in the qualifying round at last year's U.S. Open, made history with her victory as the first Canadian to ever win a Grand Slam title.

The U.S. Open crowd was clearly in Williams' favor -- leading Andreescu at one point in the match to cover her ears -- but the Canadian star is beloved in her home country and she said she felt the support "200%."

PHOTO: Serena Williams and Bianca Vanessa Andreescu during the womens trophy ceremony at the 2019 US Open at Billie Jean National Tennis Center in New York City, Sept., 7, 2019. Dubreuil Corinne/ABACAPRESS.COM via Newscom
Serena Williams and Bianca Vanessa Andreescu during the women's trophy ceremony at the 2019 US Open at Billie Jean National Tennis Center in New York City, Sept., 7, 2019.

Andreescu received tweets of support from the NBA champs Toronto Raptors and Canadian Prime Minister Justin Trudeau, to name a few.

"I’ve been feeling all the love, not only this past week but this whole year," said Andreescu. "It’s been really nice to have all that support ... I have no idea how to repay everyone for that."

Andreescu's first reaction to her U.S. Open, she said, was that "all of that hard work paid off." That hard work included sacrifices from her parents, Nicu and Maria Andreescu, who emigrated from Romania to Canada, where Bianca Andreescu was born.

One of Andreescu's goals on the pro tour has been to make enough money so that her parents can travel with her more on the road. She took home $3.85 million with her U.S. Open win.

PHOTO: 2019 U.S. Open champion Bianca Andreescu speaks with Robin Roberts on Good Morning America, Sept. 9, 2019. ABC News
2019 U.S. Open champion Bianca Andreescu speaks with Robin Roberts on "Good Morning America," Sept. 9, 2019.

And Andreescu said while she's enjoying the "hectic" attention after her victory, she plans to get back on the court and keep winning more titles.

"This is truly like an amazing accomplishment but I could definitely get used to this feeling. I’m not done yet," she said, while holding the U.S. Open trophy. "Having my name amongst all these amazing champions is amazing so hopefully I can just keep it going."