Hopes were good for Tomljanovic on Wednesday following her victory in straight sets over Veronika Kudermetova the previous day.
Particularly as Swiatek had been beaten in three sets in her last match at the end of July, by eventual winner Caroline Garcia in the quarterfinals of the Poland Open.
But 21-year-old Swiatek, who is enjoying a stellar year, broke twice in the opening set on her way to a 6-1 6-2 victory.
Although Tomljanovic, the world No.72, broke twice herself in the second set, she could not hold her own serve even once as Swiatek moved through serenely into the last 16.
American Coco Gauff outlasted Wimbledon champion Elena Rybakina 6-4 6-7 (10-8) 7-6 (7-3) in a marathon clash, while Czech Karolina Pliskova outclassed Amanda Anisimova 6-1 6-1.
Gauff, the 18-year-old French Open finalist, cruised through the first set with four aces, breaking Rybakina in the seventh game, and appeared to have the match firmly in hand.
But Rybakina refused to go down without a fight, fending off four match points in the second-set tiebreaker before taking it.
A rattled Gauff struggled in the third set, stumbling into seven double faults as the two players exchanged breaks of serve.
The American then dug deep, winning five straight points to clinch the third-set tiebreaker.
Former world number one Pliskova had no such issues against American Anisimova, breaking her in the fourth game of the first set before running away with the match.
Pliskova fired down seven aces and won nearly three quarters of her first-serve points, just a f ew days after Anisimova bounced her out in the second round of the Silicon Valley Classic.Â
She next faces Greek powerhouse Maria Sakkari.
Two-time Grand Slam winner Simona Halep of Romania eased past China's Zhang Shuai 6-4 6-2.
With agencies
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