Birrell came from behind in a three-set thriller to beat world number 10 Daria Kasatkina 5-7 6-4 7-6(3) in three hours and eight minutes. 

"It still hasn't really sunk in. I'm just really excited that I get to play again. I'm on a massive high at the moment," Birrell said.

"I don't know if I can put it into words."

In hot and humid conditions at the Queensland Tennis Centre, the Gold Coast-born player went ahead early in the opening set before Kasatkina showed her experience to level the scores and take the advantage. 

However, Birrell didn't give up and won the second to force a third. 

The crowd built around Show Court 1 with an 'Aussie Aussie Aussie Oi Oi Oi' ringing out when the 20-year-old wildcard came from 3-5 down to level the scores. 

With neither player able to get up by two, it was off to a tie-break. There were nerves all-around the crowd when Birrell used her last review on what looked to be the right call by the umpire but turned out it wasn't and everyone blew a sigh of relief. 

However, once Birrell got the ball rolling she quickly racked up the points to win the tiebreak and the match. It was her first win over a top-10 opponent and second ever WTA main-draw victory. 

For Aiava, she continued love affair with the Brisbane International as she took down former top-tenner Kristina Mladenovic 6-4 7-6(3).

The 18-year-old made a stunning debut at the tournament two years ago when she won throughout qualifying before falling to Svetlana Kuznetsova in the second round.

She now faces US Open Champion Naomi Osaka tomorrow. 

"I'm looking forward to the experience and getting out on Pat Rafter for the first time as well in a night match. So I'm looking forward to it," Aiava said.