The match otherwise began brightly for the Dane, but she was unable to maintain her initial high level, and in the decisive third set, Tauson suffered from back problems, which clearly hampered her movement.
It is the second time within a week that physical problems have proved to be a huge obstacle for Tauson. Last week, it was the hip that caused problems when the Dane had to withdraw in Wuhan against Italian Jasmine Paolini.
Tauson appeared to have put those hip problems behind her from the start on Tuesday morning. She moved well around the court against Tomljanovic, and especially her forehand and volleys looked sharp.
At the same time, Tomljanovic delivered a large number of unforced errors, and ahead 5-1, the Dane had no trouble serving home the first set.
From the start of the second set, it looked like the Dane would continue in the same style, but after a quick break, Tomljanovic woke up.
The Australian added stability to her game, Tauson lost her rhythm and started making a lot of unforced errors as Tomljanovic opened up a 4-1 lead.
Tauson did manage to break back and restore parity, but as the second set was decided in a tiebreak, Tomljanovic prevailed to take the game into a decisive set.
The third set was more uneven, with both players struggling in their own service games.
Trailing 2-3, Tauson was in obvious pain as she was forced to take a medical timeout to get treatment on her back. Tauson was visibly very restricted in her movements, which forced her to go for big shots, but it also led to more unforced errors.
Ahead 5-3, Tomljanovic took advantage of her second match point to close out the match against the disappointed Dane.