The late-blooming O'Connell caused a major upset early on day four of the Australian Open by downing No.13 seed Diego Schwartzman 7-6 (8-6) 6-4 6-4, while Inglis overcame a second-set blip to oust American qualifier Hailey Baptiste 7-6 (7-4) 2-6 6-2.

It guarantees the unheralded Australians $221,000 each in prize money, even if they bow out in the round of 32.

After claiming a marathon opening set in a tiebreak, O'Connell continued to play the big points better against Schwartzman.

"It's the best feeling I've ever had on a tennis court and I've been playing tennis since I was four," said O'Connell.

"To have moments like this, it's a dream come true.

"It's a little corny, but that's what it is."

O'Connell's next opponent will be American serve-volleyer Maxime Cressy, who at 198cm will provide a completely different physical challenge to the 170cm counter-puncher Schwartzman.

"It's going to be interesting," said O'Connell.

"I played (towering American John) Isner in Atlanta last year, which was an experience and I'm looking forward to playing Cressy."

Schwartmzan had reached the third round at Melbourne Park in each of the past four years and had never before lost at a slam to a player ranked as low as O'Connell, the world No.175.

But he had no answer to the Australian underdog, who was roared home to victory by a raucous home crowd on Court 3.

"Last year when I played on that court I felt like I didn't really look around - I was just in my own little world," O'Connell said.

"But this time I really tried to just take it all in, to look around and really feed off the crowd energy."

The atmosphere was just as charged over on Margaret Court Arena as the 24-year-old Inglis took control in the third set against Baptiste.

After reeling off the last six games to clinch the victory, Inglis fell to her knees and shook her head in disbelief.

Having lost her first four matches at the majors spread over a five-year period, the world No.133 has now won two in the space of three days, all while earning a career-changing financial boost.

"Im just enjoying the moment, enjoying being here at a slam," she said.

"This is my favourite tournament.

"... I actually didn't know the amount until somebody just said something in the interview before this.

"It is incredible, but the prize money is something that I try really hard not to think about.

"I haven't done that at this tournament very much at all, which I think has helped me.

"But it's going to be a huge help for me this year - it's going to take a little bit of pressure off me financially."

In another big opportunity, Inglis's third-round opponent will be unseeded Estonian veteran Kaia Kanepi.

AUSTRALIANS IN ACTION ON DAY FIVE (PREFIX DENOTES SEEDING)

Men's singles, third round

1-Ash Barty v 30-Camila Giorgi (ITA)

Australian Associated Press