In the fourth round, Raducanu lost only three games in her victory over Shelby Rogers of the USA who had beaten the top seeded Wimbledon champion Ash Barty of Australia in the previous round.
Raducanu then beat the newly crowned Olympic gold medalist and 11th seeded Belinda Bencic in the quarterfinals before also upsetting the 17th seeded Maria Sakkari of Greece in the semifinals.
In the final versus the 19 year old Fernandez who herself enjoyed a breakout tournament, Raducanu held serve to lead 1-0 before breaking serve to lead 2-0.
Fernandez broke back to level the set at two games all before Raducanu executed more aggressive serving and groundstrokes to hold serve and lead 5-4.
With Fernandez serving to stay in the set, Raducanu struck a crosscourt backhand return winner before also striking a down the line forehand winner to break serve and take the set.
Fernandez scored the first break of serve in set two to lead 2-1 before Raducanu struck two consecutive crosscourt backhand winners to break serve and level the set at two games all.
Raducanu held serve to lead 3-2 before striking a down the line forehand passing shot winner on breakpoint in the following game to lead 4-2.
Following two holds of serves, Raducanu served for the match at 5-3.
The Brit then powered to matchpoint after striking another down the line forehand winner which she followed up with an overhead winner.
Raducanu, cheered on at Arthur Ashe stadium by British tennis greats Virgina Wade and Tim Henman struck an ace out wide, her 23rd winner for the day then fell to the court in celebration before hugging Fernandez at the net.
Ranked number 338 in June when she received a Wimbledon wildcard and number 150 upon entering the US Open, Raducanu made her impossible run in New York City in only her second career grand slam event.