Defending champion Rafael Nadal and women's favorite Iga Swiatek battled through to victories on day one of the Australian Open on Monday.
Nadal was the headline act as the first Grand Slam of the year, which runs through to January 29, started in Melbourne amid warm and sunny conditions.
The 36-year-old Spaniard prevailed in a gruelling match against Jack Draper of Britain with an unconvincing 7-5, 2-6, 6-4, 6-1 victory.
Nadal had 46 unforced errors but wore down 21-year-old Draper, who labored with an upper right leg injury which required treatment.
It was enough to move into the second round where he will play Mackenzie McDonald, who beat fellow American Brandon Nakashima in five sets.
But doubt remains over Nadal's chances of a record-extending 23rd Grand Slam title after coming into the tournament with form and injury concerns.
"It's a victory I needed. I played against one of the toughest opponents possible in the first round," Nadal said. "He's young, he has the power and I think he has a great future in front of him."
Third seed Stefanos Tsitsipas beat France's Quentin Halys 6-3, 6-4, 7-6 (6) and continued his red-hot start to the year, where he hasn't dropped a set.
"It was challenging, he came up with some good tennis in the third set," said Tsitsipas, who is seeking an elusive Grand Slam title.
"I think my fighting spirit showed towards the end. I wasn't going to give up."
Daniil Medvedev, an Australian Open finalist in the last two years, made an impressive start with a 6-0, 6-1, 6-2 thrashing against American Marcos Giron.
But 2014 champion Stan Wawrinka was knocked out by Slovak Alex Molcan 6-7 (3), 6-3, 1-6, 7-6 (2), 6-4.
Leading Australian player Nick Kyrgios pulled out of the tournament due to a knee injury a day before he was due to face Russian Roman Safiullin in the first round.
Kyrgios' withdrawal is a further blow to a tournament without a host of marquee players.
The polarising Wimbledon finalist has been one of the drawcard players in his home Grand Slam over the years and was deemed an outside chance of winning his first major title.
In the women's draw, 21-year-old Swiatek was made to work in the night session with a 6-4, 7-5 victory over German Jule Niemeier.
The Pole was broken in the opening game of the second set before clawing back to claim the two-hour contest.
No. 3 seed Jessica Pegula of the United States had few worries in her 6-0, 6-1 thrashing over 161st-ranked Romanian Jaqueline Cristian.
Sixth seed Maria Sakkari of Greece defeated China's 24-year-old Yuan Yue 6-1, 6-4.
No. 7 seed Coco Gauff had a comfortable 6-1, 6-4 victory over Katerina Siniakova of the Czech Republic. The American breezed through the first set but was made to work in the second set and broken in the sixth game.
But she rallied to win the next four games to wrap up the win in 75 minutes.
Former Australian Open champion Sofia Kenin of the United States crashed out in straight sets to Victoria Azarenka, who is now the only player left in the women's draw to have won the title at Melbourne Park after victories in 2012 and 2013.
China had several notable successes on the opening day of competition.
17-year-old Shang Juncheng made a spectacular Gram Slam debut with a 6-2, 6-4, 6-7 (2), 7-5 victory over Germany's Oscar Otte.
Shang, who became the youngest player in the men's draw after emerging from qualification, created history by becoming the first men's player from mainland China to register a victory at the Australian Open's main draw since the Open Era started in 1968.
Compatriot Wu Yibing lost a five-set thriller to France's Corentin Moutet.
Zhu Lin, Wang Xinyu and No. 29 seed Zheng Qinwen, won in the women's draw.
Men's favorite Novak Djokovic of Serbia and women's No. 2 seed Ons Jabeur of Tunisia will headline day two action.
