World number one Simona Halep survived an almighty scare against Sofia Kenin before she overcame the unseeded American to reach the third round.
After blasting her way through the first set and racing to a 3-0 lead in the next, 2018 runner-up Halep appeared to step off the gas as she allowed the determined Kenin to level at 3-3 and eventually drag the contest into a decider.
Halep, who lost the final at Melbourne Park last year, was down a break at 2-4 in the deciding set but showed poise under pressure to claw her way back.
Halep regained control with a decisive break in the ninth game before closing out the match on her second match point in two hours and 31 minutes. She prevailed 6-3 6-7(5) 6-4 and will meet Venus Williams in the third round. Williams beat Frenchwoman Alize Cornet 6-3 4-6 6-0.
The Romanian has struggled for form and fitness since her first-round defeat at the United States Open last August and came into the year's first Grand Slam short of preparation after a back injury ended her 2018 season prematurely.
The French Open champion said in her post match interview that she injured herself during the second set.
"I have no idea how I won," the 27-year-old said. "It was a very tough one - she is an amazing player."
Australian wildcard advances as seventh seed forced to retire
Another Australian teen sensation Alexei Popyrin is into the third round of the Australian Open after Dominic Thiem retired midway through the third set of their Melbourne Arena clash.
The 19-year-old surprise packet was well on top before the Austrian seventh seed and 2018 French Open finalist called it quits while trailing 7-5 6-4 2-0.
Thiem, who had a five-set first round win, called for the trainer midway through the second set citing general fatigue.
Wildcard Popyrin, who had only played one grand slam match before this tournament, looked fearless. Using his big forehand weapon, Popyrin hit almost double the winners of Thiem, who looked sluggish from the outset.
Despite standing 195cm Popyrin showed impressive speed around the court as he pressed the tiring Thiem. Popyrin said he felt in control after wrapping up the second set.
"It is never easy winning like this - Dominic played a tough first round," Popyrin said.
"I always thought that I was in the match to be honest but when I won the second set is when that thought really kicked in and that I could actually win the match."
- AAP / Reuters