In 2015, Bianca Andreescu wrote herself a cheque for winning the US Open. This week, she won it.

You’d be forgiven if you have never heard of Bianca Andreescu, the US Open 2019 women’s champion.

In 2018, Andreescu didn’t even qualify for the grand slam tennis tournament.

But on Saturday, in an astounding execution of athleticism and mental strength, the 19-year-old won her first grand slam championship in straight sets against one of the best tennis players of the era, Serena Williams.

She will take home US $3,850,000 (about AU $5,083,000).

So, how did she do it?

According to her, it’s due to visualisation techniques.

After winning Orange Bowl, a prestigious junior title, in 2015 at age 15, Andreescu realised the unlimited potential of her talent.

She wrote herself a mock cheque, visualising herself as the US Open champion. Each year, she recalls updating the cheque with the new prize money total.

And on Saturday, she no longer had to pretend. She was holding the coveted trophy, cheque in pocket.

who is Bianca Andreescu
"I’ve been dreaming of this moment for the longest time." Image: Getty.

"It’s so crazy," Andreescu says in her winner's press conference, placing her head in her hands as she comes to terms with the victory.

"I’ve been dreaming of this moment for the longest time. Like I said after I won the Orange Bowl, a couple months after, I really believed that I could be at this stage.

"Since then, honestly I’ve been visualising it almost every single day. For it to become a reality is just so crazy. I guess these visualisations really, really work."

Bianca's stunning and sudden rise to the top has also been thanks to an attitude adjustment, she says.

"I don't think I was ever as composed as I am now. I would get really down on myself and I would get very negative thoughts going through my mind, I would smash rackets, I would yell at myself even during practice."

She continued: "But I found that way wasn't working to my advantage at all and so I started seeking some advice and ever since then I've been trying to have a very positive outlook on everything and I think that's really been helping me."

Who is Bianca Andreescu?

Bianca Andreescu is the first person born in the 2000s to take home a grand slam trophy.

She was born in Ontario, Canada before moving back to her parents' homeland of Romania as a toddler. The family then returned to Canada - so the story goes - with only two suitcases and a dream when the budding tennis champion was 11. She is living out the dream barely eight years later.

At the start of 2019, Andreescu was ranked 178th in the world. Now, she is the first Canadian to win a singles grand slam and will rocket to No. 5 seeding on Monday courtesy of her three titles, winning 45 from 49 matches and now a maiden major in a spectacular breakout season.

- With AAP.

Sign up for the "Mamamia Daily" newsletter. Your morning hit of the top news stories, to be consumed with a coffee in hand.