Top dogs Alcaraz and Swiatek back in action at Australian Open
Spanish world number two Alcaraz was in scintillating form as he blew away veteran Richard Gasquet in his opening match, unleashing 53 winners.
The 20-year-old showman admitted after his straight-sets win that he sometimes tries to play "impossible shots", including volleys and drop shots, to please his supporters.
Alcaraz, who missed the 2023 Australian Open due to injury, is aiming to become the third man in the Open Era to win three Grand Slams before the age of 21, after Bjorn Borg and Mats Wilander.
He also has the chance to supplant Novak Djokovic as world number one.
The two-time Grand Slam champion, who has never been beyond the third round in Melbourne, faces Italy's Lorenzo Sonego, who won their only previous encounter, in 2021.
But Sonego said Alcaraz was now a different player.
"He's aggressive on court. He stays near to the baseline, and he wants to be aggressive. He has a good touch, good volley, good return."
Women's world number one Swiatek had a tough first-round match in Melbourne against former Australian Open champion Sofia Kenin but came through to extend her winning run to 17 matches.
The Polish player, 22, lost to Collins in the 2022 semi-finals in Melbourne but Swiatek has won their other four meetings, including three last year.
"For sure I can't say that I have an easy draw here," Swiatek said. "I'll try to do my best. Danielle is a really good player.
"We played really tight matches. On the other hand our last match was pretty -- I mean, from the score, I had it under control."
Elsewhere on day five at Melbourne Park, Kazakh third seed Elena Rybakina, last year's defeated finalist, takes on unseeded Russian Anna Blinkova and fifth seed Jessica Pegula faces France's Clara Burel.
Former US Open champion Emma Raducanu, playing her first Grand Slam for a year after an injury-wrecked season in 2023, is up against China's Wang Yafan.
"I honestly didn't know if I'd ever get to this stage," the 21-year-old British player said after her first-round victory against America's Shelby Rogers.
In the men's draw, third seed Daniil Medvedev is in action against Finland's Emil Ruusuvuori, while German sixth seed Alexander Zverev takes on Slovakia's Lukas Klein.
