Defending champion Caroline Wozniacki saved a break point in the opening game but there was little trouble to follow as she beat Alison Van Uytvanck 6-3, 6-4 in the first round. Wozniacki, who saved both break points she faced, clinched the match on her third match point with a forehand to the open court.
The third-seeded Wozniacki beat Simona Halep in last year's final to capture her first major title.
Australian Open 2019: Rafael Nadal, Maria Sharapova advance after straight-sets victories on the opening day
Wozniacki opened night play at Rod Laver Arena, where three tournament champions preceded her and all won — Maria Sharapova, Rafael Nadal and Angelique Kerber.
Second-seeded Angelique Kerber is through to the second round at Melbourne Park with a 6-2, 6-2 win over Polona Hercog.
The 2016 champion needed just 72 minutes to beat the Slovenian player, saving all four break points she faced and winning four of five break points on Hercog's serve.
Kerber became the first German woman since Steffi Graf at the 1999 French Open to win a major when she beat Serena Williams in the final here three years ago.
Maria Sharapova got out of the Melbourne heat as quickly as she could, needing just 63 minutes to beat British qualifier Harriet Dart 6-0, 6-0 in the first match on Rod Laver Arena at this year's Australian Open.
Sharapova, who wore an ice collar during breaks to help alleviate the 30 degree Celsius (86 Fahrenheit) temperature, was making her 15th appearance at the season-opening major.
The only break point Sharapova faced was when she double-faulted in the fifth game of the second set.
Two-time Wimbledon champion Petra Kvitova was shunted from a show court to a side court at Melbourne Park late in the day but it didn't matter where she was — the Czech player beat Magdalena Rybarikova 6-3, 6-2 in 67 minutes.
Fifth-seeded Sloane Stephens ended a three-match losing streak in first-round matches at Melbourne Park with a 6-4, 6-2 win over fellow American Taylor Townsend.
Stephens lost in the first round of the Australian Open in 2015, 2016 and 2018. She missed the 2017 tournament here after undergoing foot surgery and went on to win the U.S. Open later the same year.
Stephens and Townsend were among 15 American women in the singles main draw this year, including those who qualified.
Townsend has lost all three first-round matches she has played in Melbourne.
Local favorite Ashleigh Barty fell behind 2-0 early and then won the next six games on her way to a 6-2, 6-2 win over Luksika Kumkhum at Margaret Court Arena.
Barty, who lost last week's Sydney International final to Petra Kvitova, beating No. 1-ranked Simona Halep along the way, broke the Thai player's serve to take a 3-2 lead in the second set, held and then took a 5-2 lead with her second break of the set.
She clinched the match with a forehand to the open court in 57 minutes.
Katie Boulter started celebrating a bit too soon during her first-round win over Ekaterina Makarova at Melbourne Park. Blame the new tiebreaker being used for the first time this year at the tournament.
Boulter beat Ekaterina Makarova 6-0, 4-6, 7-6 (6), including 10-6 in the tiebreaker. But the British player started celebrating and went to the net when she reached 7-4 in the tiebreaker , forgetting the third-set decider wasn't using a conventional count.
The new rule is first to 10 with a two-point cushion was introduced to ensure matches don't get too lengthy — previously the third set in women's matches and the fifth set in men's matches at the Australian Open had to be decided by a two-game advantage.
Katie Boulter has the distinction of winning the first 10-point tiebreaker under the Australian Open's new system for determining level deciding sets.
Boulter beat Ekaterina Makarova 6-0, 4-6, 7-6 (6), including 10-6 in the tiebreaker in which the first player to reach 10 with an advantage of two points clinches the match.
In the men's singles draw, the first four sets will feature a seven-point tiebreaker at 6-6, with the final set going to a 10-point tiebreaker at 6-6.