Playing in her first Grand Slam since pulling out of the French Open earlier this year, Osaka's return to Flushing Meadows did not go to plan, as she wordlessly left the court after uncharacteristically losing her cool in the second set tiebreak.
There were no signs of trouble in a routine opening set won by Osaka before things began to unravel late in the second when Fernandez broke her at 6-6 to force a tie-break.
As the Canadian took control Osaka threw her racquet across the court.
Umpire Alison Hughes was willing to give Osaka a pass for this act for which many players would have received a code violation, but in the third set with Fernandez serving to go up 2-0 she finally issued a warning when the former-world number one angrily smashed the ball into the stands.
Osaka was unable to trouble Fernandez in the rest of the match, with the Canadian sealing victory when Osaka hit a forehand wide.