As a 19-year-old, she finished runner-up at the 2021 US Open to fellow teenager Emma Raducanu, defeating three top-5 players en route to the final, including defending champion Naomi Osaka.

Fernandez played a pivotal role in Canada's first-ever Billie Jean King Cup win in 2023, defeating Jasmine Paolini in the final.

[3] On 25 January 2019, as a 16-year old, Fernandez reached the Australian Open girls' singles final, where she lost to the top-seeded Clara Tauson.

[4] On 8 June 2019, Fernandez defeated Emma Navarro in the French Open final to become the first Canadian female winner of a junior Grand Slam title since Eugenie Bouchard at the 2012 Wimbledon Championships,[3][5][6] a victory that earned her the world No.

[7] On 21 July 2019, Fernandez won her first professional singles tennis title when she rallied to beat fellow Canadian Carson Branstine in the final of the Gatineau Challenger!

The pair defeated the second-seeded team of Marcela Zacarías of Mexico and Hsu Chieh-yu of Taiwan.

[8] The following week, she made her second consecutive ITF final in Granby,[9] losing to Lizette Cabrera of Australia.

[10] She achieved the biggest win of her career the following week in the 2020 Billie Jean King Cup qualifying round against world No.

[11] In late February, at the Mexican Open, she qualified and reached her first WTA Tour final, losing to world No.

However, in March at the Monterrey Open, she won her first four matches to reach the final, defeating Viktorija Golubic to win the first WTA Tour title of her career.

[28] Fernandez started the season at the Adelaide International where she advanced to the round of 16, in which she was defeated by Iga Świątek, in straight sets.

In her third-round match, she won the second-set tiebreak and defeated Shelby Rogers in three sets, before losing to defending champion Paula Badosa in the fourth.

[34] In the doubles competition, partnering with Alizé Cornet, the pair reached semifinals losing there to eventual champions Xu Yifan and Yang Zhaoxuan.

[36] A Grade-III-fractured foot acquired during her quarterfinal match with Trevisan forced her to miss Wimbledon, after a first-round exit the previous year to Jeļena Ostapenko.

[43] At the Miami Open in the doubles competition, partnering with Taylor Townsend, they reached the final where they lost to American No.

Fernandez was knocked out of the US Open in the first round by Ekaterina Alexandrova,[47] but again with Townsend, reached the quarterfinal of the women's doubles losing to eventual champions, Erin Routliffe and Gabriela Dabrowski.

[48] At the beginning of the Asian swing, Fernandez failed to qualify for the China Open, but won her first title since February 2022 at the Hong Kong Open, defeating Victoria Azarenka, Mirra Andreeva, Linda Fruhvirtová, Anna Blinkova and Kateřina Siniaková.

[51] This was Canada's first ever Cup win, immediately hailed as a major moment in the history of Canadian tennis, and Fernandez was widely singled out for praise for her contributions.

[55] At her home tournament, the Canadian Open in Toronto, she reached the doubles semifinals with her sister Bianca where they lost to Gabriela Dabrowski and Erin Routliffe.

[60] Partnering with Yulia Putintseva, Fernandez reached the final of the doubles at the same event but the pair lost to Asia Muhammad and Erin Routliffe in a champions tie-break decider.

[64] At the Abu Dhabi Open, she was seeded eighth and overcame lucky loser Moyuka Uchijima[65] and Lulu Sun[66] to make it through to the quarterfinals, where she lost to Ashlyn Krueger.