Rafael Nadal launched his Australian Open title defence with a four-set victory over Britain's Jack Draper as home hope Nick Kyrgios exited through injury without hitting a ball.
In the women's draw, in-form Jessica Pegula and teenage prodigy Coco Gauff were both emphatic winners on the first day of the opening Grand Slam of the year.
Spanish great Nadal, 36, had been in poor form by his sky-high standards, losing six of his last seven matches stretching back to defeat in the last 16 at the US Open.
In fast-rising Draper, 21, the 22-time Grand Slam champion faced a tough test to start his campaign at a sweltering Melbourne Park.
But top seed Nadal recovered from a second-set wobble to defeat the 38th-ranked Briton 7-5, 2-6, 6-4, 6-1 at Rod Laver Arena.
Nadal, who is now a father, faces American Mackenzie McDonald in round two.
"Very exciting, new beginning, just super-happy to be back at Rod Laver with a victory I needed," he said after seeing off Draper.
"Last couple of months have not been easy for me... a very positive start."
Nadal was on court when Australia's talented but temperamental Kyrgios called a hastily arranged press conference and announced that he was out with a knee injury.
"I'm devastated, obviously," said the Wimbledon finalist, who was considered an outside bet to win a maiden Grand Slam crown.
"I've had some great tournaments here, winning the doubles last year and playing the tennis of my life probably going into this event.
"I'm just exhausted from everything, and (it's) obviously pretty brutal."
The Australian Open had already lost several stars in the build-up.
Injured men's world number one Carlos Alcaraz and two-time Melbourne champion Naomi Osaka -- who is expecting her first child -- are among the other high-profile players missing. Nine-time Australian Open champion Novak Djokovic, who was detained and deported ahead of last year's tournament after refusing to get vaccinated for Covid, begins his title assault on Tuesday.
Other winners in the men's draw on Monday included teenager Shang Juncheng.
The 17-year-old, the youngest player in the men's draw, created a slice of history by becoming the first men's Chinese player to win an Australian Open main-draw singles match. The teenager battled past Germany's Oscar Otte in nearly three hours and four sets to progress.
He faces American 16th seed Frances Tiafoe next.
Other winners included 18th seed Karen Khachanov, 10th seed Hubert Hurkacz and Italian 15th seed Jannik Sinner. But 21st seed Borna Coric fell to Czech player Jiri Lehecka in straight sets.