A big day for Aussie tennis, with four players in the last-16 draws for the first time since 1999, was tinged with disappointment as both Alex de Minaur and Jason Kubler were knocked out in the fourth round.

But the Kyrgios-Tomljanovic double made it the first time since Jelena Dokic, Pat Rafter and Mark Philippoussis in 2000 that Australia could celebrate both men's and women's players in the quarter-finals.

Kyrgios took on the men's mantle of 'Aussie battler' by scrapping into the quarters on a day when his famed volatility was replaced by stubborn bloody-mindedness on centre court as he tamed American Brandon Nakashima in five sets while nursing a shoulder injury.

Then Kyrgios's former girlfriend Tomljanovic, so often burdened by her own lack of self-belief, produced one of the gutsiest performances of her career to slay Wimbledon's very own giant-killer Alize Cornet and reach the last eight for the second year in a row.

No Australian woman has achieved that feat since Dokic 22 years ago, and Tomljanovic brought a lump to the throats of the fans on court 2 as she declared after her tears subsided: "I didn't really think I could do it ..."

De Minaur and Kubler, the archetypal 'Aussie battlers', had to hand over that crown for a day to Kyrgios, who produced, by his glittering standards, a subdued performance with few fireworks - and no controversy - but still wrestled his way to a first grand-slam quarter-final since the 2015 Australian Open.

The only disappointment after his 4-6 6-4 7-6 (7-2) 3-6 6-2 win over rising 20-year-old Nakashima was he wouldn't be able to play his Sydney pal and Aussie No.1 de Minaur in the last eight.

"I was really excited to play de Minaur to be honest. He's been flying the Aussie flag for so long and he was two sets up when I came on court," said Kyrgios, who'd been hoping Australia might get three men into the Wimbledon quarters for the first time in 51 years.

But de Minaur relinquished a two-set advantage, then was unable to convert either of two match points in the deciding set of a crushing 2-6 5-7 7-6 (7-3) 6-4 7-6 (10-6) loss to the unseeded Chilean Cristian Garin.

Kubler's dream run through the qualifiers to his first-ever grand slam quarter-final was then ended in perhaps predictably brutal fashion as he was taken to school by big-hitting American 11th seed Taylor Fritz 6-3 6-1 6-4.

But Kyrgios cast aside the showman's cloak to knuckle down to his win, which was a mercifully mellow affair compared to the mayhem that had enveloped his previous barn-burner with Stefanos Tsitsipas.

"I knew from the get-go I wasn't playing as well as I would have liked. I knew I had to keep my head down and just battle today. It was a good mental performance," said Kyrgios.

Tomljanovic must have been proud of hers too, as she had to come from a set down and hold off a late rally from the indomitable Cornet, conqueror of world No.1 Iga Swiatek in the previous round, before winning 4-6 6-4 6-3.

The 29-year-old will next tackle talented Kazakh left-hander Elena Rybakina, who beat her on clay in their only meeting in Madrid last year.

"After last year, facing Ash (Barty in the quarter-finals), I can face anyone," beamed Tomljanovic, who's making good viewing for the Netflix tennis documentary crew following her rejuvenating run.

Australian Associated Press