Simona Halep climbed out of a deficit of a set and a break to avoid becoming the first No. 1-seeded woman to lose in the Australian Open's first round in 40 years.
Halep reeled off the last four games, and 13 of the final 15 points, to come back and beat Kaia Kanepi 6-7 (2), 6-4, 6-2.
Australian Open 2019: Rafael Nadal, Maria Sharapova advance after straight-sets victories on the opening day
Kanepi received treatment from a trainer for a blister on her left ring finger in the third set.
Kanepi had beaten Halep at the U.S. Open in September, only the sixth time in the professional era that a woman seeded No. 1 exited a Grand Slam tournament in the opening round.
Naomi Osaka's first appearance at a Grand Slam tournament as a major champion was a successful one. She beat Magda Linette 6-4, 6-2 to end play at Rod Laver Arena on day 2 of the Australian Open.
Osaka, who beat Serena Williams in last year's U.S. Open final, needed just 58 minutes for her first-round win over Linette.
Her win at Flushing Meadows last year as a 20-year-old made her the youngest U.S. Open champion since Maria Sharapova in 2006.
Osaka's next opponent will be Tamara Zidansek, who beat Daria Gavrilova 7-5, 6-3 earlier Tuesday.
Things were looking bad for Venus Williams, who was perilously close to an opening-round exit at the Australian Open for the fourth time in six years.
When she double-faulted twice in the span of three points, Williams suddenly trailed by a set and a break against 25th-seeded Mihaela Buzarnescu. At that moment, 1½ hours into the match, all that separated Williams from defeat was one game. Just one.
And over the next 70 minutes Tuesday, Williams went from nearly gone to moving on, putting together a 6-7 (3), 7-6 (3), 6-2 victory over Buzarnescu to reach the second round in Melbourne.
Tenth-seeded Daria Kasatkina has lost 6-3, 6-0 in the first round of the Australian Open to Timea Bacsinszky.
Kasatkina, who reached the quarterfinals at the French Open and Wimbledon and broke into the top 10 last October after winning a title in Moscow, struggled with her serve and had nine double-faults in the 55-minute defeat.
It was the third consecutive tournament in Australia where Kasatkina lost in the first round following her early exits at the Brisbane International and the Sydney International.
Eugenie Bouchard advanced to the second round at Melbourne Park with a 6-2, 6-1 win over wild-card entry Peng Shuai.
Peng saved one match point on her serve but a backhand wide gave the Canadian another, and Bouchard clinched the 59-minute match with a forehand to the open court.
The 2014 Wimbledon finalist's ranking dropped from a career-high of five to a current 79 to start 2019 after a series of injuries and poor form.
Bouchard, who also made the Australian Open and French Open semifinals in a breakthrough 2014, will be severely tested in her second-round match Thursday when she plays 23-time Grand Slam singles champion Serena Williams.
(With AP Inputs)