Australia's teenage starlet lost 6-3 6-3 in one hour 20 minutes on a baking 30C degree day in Washington.
Joint will be going to Flushing Meadows amid raised expectations after an impressive first half of the season - and the knowledge that last year she came through qualifying and reached the second round in New York.
Defeat robbed her of useful match practice on the hardcourts but having been born in Michigan and lived there until she was 16 the 19-year-old is well versed on the surface in north America.
It is a measure of her progress that this time last year Joint was playing WTA 125s and ITF events in Europe.
She then played a couple of ITFs in America before entering US Open qualifying.
This year she will gain direct entry to the main draw at at Flushing Meadow having risen 97 places in a year to 38th in the world.
Fernandez is ranked two places higher, but the gap looked bigger as she dominated their first meeting on a very sparsely attended Stadium court.
Perhaps deflated by the lack of atmosphere Joint rarely troubled her 22-year-old opponent, forcing one break point, which she failed to take.
Fernandez, who reached the US Open final in 2021 but has only won one main draw match in New York since, was ahead on most metrics, notably serving in which she hit five aces to Joint's none, while the Australian double-faulted five times and the Canadian twice.
Joint is the only Australian in the WTA 500 event, which has Americans Jessica Pegula, who Fernandez will now play, and Emma Navarro as top seeds.
The main attractions, though, are the returning Venus Williams and two-time US Open champ Naomi Osaka, both of whom start their campaign on Tuesday.
Williams has added her name to the US Open mixed doubles list, paired with Reilly Opelka, with Wimbledon runner-up Amanda Anisimova also putting her name forward partnering Holger Rune.
As they suggested at Wimbledon, Alex de Minaur and his fiancee Katie Boulter have also entered the new-style format.
There are now 25 duos on the entry list with the deadline a week away. The top eight pairs with the highest combined singles rankings will gain entry along with eight wild-card partnerships. The latter could include Naomi Osaka and Nick Kyrgios who have applied.
Meanwhile, in Europe, Astra Sharma lost in the first round of the WTA 250 in Prague, beaten 7-6 (8-6) 6-3 by American ninth seed Ann Li.
Other seeds Rebecca Sramkova (2), Marie Bouzkova (5) and Alycia Parks (8) also went through.
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