New York, NY, USA, 31 August 2018 | Darren Walton/AAP

Australian Alex de Minaur made a fuss-free entry to the third round of the US Open in New York on Thursday.

The teenage ace could hardly have been more impressive in taking out highly rated young American Frances Tiafoe 6-4 6-0 5-7 6-2 to reach the the last 32 for the second successive Grand Slam, after doing so at Wimbledon in July.

De Minaur joins fellow Australians John Millman and Nick Kyrgios, who both won earlier on Thursday, and Ash Barty in the last 32 in New York.

Ajla Tomljanovic fell to Czech Katerina Siniakova after an almighty battle; she served for the match at 6-5 in the third set and even had a match point, but eventually went down 6-3 6-7(3) 7-6(4).

A year older and ranked one place higher than 19-year-old De Minaur, world No.44 Tiafoe played some blinding tennis at times.

But he was soundly beaten as the Sydney-born talent showcased his relentless counter-attack, mixed with some great guile, to break Tiafoe eight times in the two-hour, 39-minute match-up.

“I had to play my best tennis today,” De Minaur said.

“All credit to Frances, I just had to be very tough throughout the whole match and try to keep my concentration and not get down on myself and always stay positive.

“That’s pretty much got me the win today.”

Even when he suffered his only lapse, losing the third set, De Minaur displayed maturity beyond his teenage years to remain focused.

“I went and changed my clothes and tried to re-set and tell myself that I am indeed two sets to one up and that I just had to play one more good set and I would get the win,” de Minaur said.

“It’s all about that positive mindset.”

De Minaur next plays Croatian seventh seed Marin Cilic, the 2014 champion, who trounced Polish qualifier Hubert Hurkacz 6-2 6-0 6-0.

That match will be played on Saturday in New York, with De Minaur gunning for a spot in the second week of a major for the first time.