With the duo’s victories, Australia has representatives in the men’s and women’s singles quarters-finals in New York for the first time since Pat Cash and Wendy Turnbull in 1984.

Nick Kyrgios again made of a mockery of the rankings and blew the US Open wide open with a rollicking fourth-round win over world No.1 and defending champion Daniil Medvedev.

Soon after, Tomljanovic snapped the 13-match, 18-set winning streak of Liudmila Samsonova with a tenacious 7-6 (10-8) 6-1 fightback against the red-hot Russian.

Just as she did in her against-the-odds win over Williams, Tomljanovic again displayed extraordinary mental resilience, this time on Louis Armstrong Stadium.

The 29-year-old battled back from 5-2 down in the opening set and saved eight set points in an epic 18-minute game to draw level at 5-5.

After fending off her eighth set point in the tiebreaker to snatch the set, Tomljanovic seemingly broke Samsonova’s spirit.

Tomljanovic said she probably would have panicked had she known the pivotal 10th game of the match lasted almost 20 minutes.

“I think it’s just about staying in the moment because she played well and I don’t really have time to dwell because the game is going by quickly,” she said.

“I’m just trying to stay as calm as long as possible even though inside I’m dying.”

Tomljanovic has now reached back-to-back grand slam quarter-finals, after making the last eight at Wimbledon six weeks ago for the second year in a row.

“It just feels really good to back up a win that got a lot of attention,” said the Australian No.1.

“Just felt like it’s been a really big 48 hours. I didn’t really feel like myself today the whole day.

“I don’t know, just felt a little bit drained. After that slow start, I just didn’t want to go out like that.

“Picked myself up, fought back really hard, played some quality tennis after that.”

Guaranteed a new career-high ranking inside the world’s top 35 after this tournament, Tomljanovic will play Jabeur on Tuesday (Wednesday AEST) after the fifth-seeded Tunisian also beat a Russian, Veronika Kudermetova, by the same 7-6 (7-1) 6-1 scoreline.

Eyeing a maiden grand slam semi-final appearance, Tomljanovic believes reaching the last eight in three of the past six majors is a bit of karma.

“It’s really nice. I think a lot of heartbreaks that have happened over a long time, I feel like this is a what-goes-around-comes-around moment for me,” she said.

“Especially the long matches that I’ve lost in the past, now I’m winning them.

“I think for that reason I’m more calm in those moments. Yeah, it just feels nice, like the work is paying off.”

-with AAP