Frances Tiafoe was the biggest casualty on a day of mixed fortunes for the United States at the Australian Open on Wednesday. 

Christopher Eubanks was also dumped out in straight sets but America's Taylor Fritz, Ben Shelton and Sebastian Korda all moved into round three in Melbourne.

Tiafoe, the No 17 seed and a quarterfinalist in Australia back in 2019, suffered a shock exit at the hands of world No 75 Tomas Machac of the Czech Republic. 

Elsewhere Eubanks was beaten 6-4, 6-4, 6-4 by No 5 seed, Andrey Rublev of Russia. Rublev hit 38 winners en route to victory in little over an 90 minutes on John Cain Arena. 

Twelfth seed Taylor Fritz was in no mood to mess around, however, slamming down 11 aces and 38 winners in his 6-0 6-3 6-1 shellacking of French qualifying lucky loser Hugo Gaston.

The 26-year-old was on Kia Arena for less than 90 minutes after surviving a five-set scare against Facundo Diaz Acosta in the first round.

'After that long one in the first round, it's great to get some time back,' Fritz said.

Fritz had never been past the round of 32 of a major until the 2022 Australian Open, when he won a five-set thriller over Roberto Bautista Agut.

Fritz booked another third-round clash at the Open with Fabian Marozsan after the Hungarian caused a 7-6 (7-5) 6-4 6-2 upset over Argentine world No.21 Francisco Cerundolo.

Meanwhile, US Open semifinalist Ben Shelton - the No. 16 seed - enjoyed a 6-4, 6-1, 3-6, 7-6 (5) over local hope Chris O'Connell.

A quarterfinalist on debut here last year, Shelton said he enjoyed the atmosphere that the home crowd gave O'Connell and said he could still hear the chant 'Aussie, Aussie, Aussie, Oi, Oi, Oi' in his sleep.

Sebastian Korda joined them in round three. The 23-year-old, seeded 29 in Australia, eased past Quentin Halys of France 6-4, 6-4, 6-4. 

He will now face Rublev, while American qualifier Aleksandar Kovacevic was beaten by Russia's No 15 seed Karen Khachanov 6-4 6-3 4-6 6-3.