Two days after spectacularly ending Serena Williams’ storied career, 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 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 cos 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.

Guaranteed a new career-high ranking inside the world’s top 35 after the Open, Tomljanovic will play either Tunisia’s fifth-seeded Wimbledon runner-up Ons Jabeur or Russian Veronika Kudermetova for a place in the semi-finals on Wednesday (Thursday AEST).

Kyrgios and Tomljanovic, a long-time former couple, are the first Australian men and women to make the US Open quarters in the same year since Pat Cash and Wendy Turnbull in 1984.

For his part, Kyrgios made 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.

In an explosive encounter laced with controversy and drama, Kyrgios risked being defaulted and overcame a running verbal battle with the chair umpire before ousting the top seed 7-6 (13-11) 3-6 6-3 6-2 on Sunday night.

It was the Wimbledon runner-up’s second defeat of Medvedev in three weeks and vaulted Kyrgios into the quarter-finals at Flushing Meadows for the first time.

“It was an amazing match,” Kyrgios said.

“Obviously Danill is defending champion. A lot of pressure on his shoulders, but I played really well. I’ve been playing amazing for the last couple of months.

“But what a place – packed house in New York, I’m extremely blessed.

“I’m just really happy and hopefully I can keep it going.”

At last realising his rich potential, the 27-year-old will play another Russian, Karen Khachanov, for a semi-final berth on Tuesday (Wednesday AEST).

“Hopefully I can go all way,” Kyrgios said before revealing he deliberately didn’t over-celebrate for that very reason.

“It’s only fourth round. I’ve got quarter-finals.

“It was an amazing experience obviously taking down the No.1 player in the world on Arthur Ashe Stadium but I don’t really like to celebrate too much after that.

“I know that if I played him nine more times, he’s probably getting on top of me the majority of the time.

“So I just take it, just get back to the right things. I just stay in the moment, and that’s it.”

Now three wins away from breaking his grand slam title duck, Kyrgios was imperious at times.

He received a standing ovation after winning a pulsating opening set that stretched more than hour.

Other times, he flirted with disaster.

He looked to have thrown away the first set after giving up a 4-2 lead and then a 4-1 advantage in the tiebreaker, not to mention threatening to hit the self-destruct button and engaging in an unnecessary, elongated exchange with Greek umpire Eva Asderaki-Moore.

The combustible Canberran lambasted Asderaki-Moore for starting the shot clock apparently too early.

“You are the only umpire that I’ve a problem in this matter,” Kyrgios fired at her.

“Use your common sense. Just use it a little bit.”

But, after regaining his cool and fighting off three set points, Kyrgios brought up a fourth of his own with an exquisite backhand drop shot that almost spun back over onto his side of the net.

But it wasn’t long before tensions really boiled over.

Medvedev fumed at the umpire for not warning Kyrgios after the Australian, frustrated at going down an early break in the second set, went within centimetres of hitting a ball into the first row of the stands, and likely a spectator.

Medvedev then threatened to quit if someone from Kyrgios’s courtside entourage wasn’t ejected for disrupting the top seed between his first and second serves.

“If they do it a second time, I am not playing they’re out, until somebody is out,” the Russian raged.

After levelling the match at a set apiece, Medvedev received an extraordinary, possibly unprecedented, gift from Kyrgios.

After looking to have earned a break point in the second game of the third set, when Medvedev couldn’t return a ball, Kyrgios ran around the net triumphantly and hit the ball away for a mock winner.

Quite rightly, though, Asderaki-Moore awarded the point to Medvedev because his shot, while clearly not going over the net, was “still in play”.

But Kyrgios, somewhat uncharacteristically, shook off the blunder before breaking Medvedev on his next service game to claim a 3-1 lead, then going on to seize a two-sets-to-one lead.

He turned the screws with two more breaks to run away with the match and claim a 20th victory in his past 23 matches after two hours, 53 minutes.