Serena Williams exploded any doubts about her form on Tuesday as she swept into the Australian Open second round on her return to Grand Slam action.

The American, with a record 23rd major title in her sights and watched by her new fiance, Reddit co-founder Alexis Ohanian, thumped dangerous Swiss teen Belinda Bencic 6-4, 6-3.

Williams has barely played since her shock defeat in the US Open semi-finals in September and she made, by one count, 88 unforced errors in her second-round loss to Madison Brengle at this month's Auckland Classic.

But she came through a tight first set against Bencic before dominating the second set in what turned out to be a convincing victory on the centre court.

"It was one of the toughest first-round matches I've ever played," said Williams, who had a 1-1 head-to-head with Bencic, 19, before Tuesday's encounter.

"Right now I've got nothing to lose. Every match, every tournament I'm playing for fun," she added.

Williams, who can break Steffi Graf's Open-era record of 22 Grand Slam titles if she wins in Melbourne for the seventh time, next faces Lucie Safarova, who had a charmed life in her win over Yanina Wickmayer.

The Czech survived nine match points before winning 3-6, 7-6 (9/7), 6-1 against the flummoxed Wickmayer, who said she was feeling "definitely not good" after letting slip so many opportunities.

"It's not fun," said the Belgian, adding: "I think she served very well on certain points and other points I didn't go for enough.

"But I think it's normal when you have match point and you want to play it a little bit safe. Then after, you realise it's not the best option."

Men's world number three Milos Raonic, a semi-finalist last year, enjoyed an uncomplicated start to his campaign when he beat Germany's Dustin Brown 6-3, 6-4, 6-2.

And German hotshot Alexander Zverev credited a racquet-smashing tantrum with sparking his revival as he came back to beat Robin Haase 6-2, 3-6, 5-7, 6-3, 6-2.

"Sometimes it's good to let it out and I started to play my best tennis again after that (racquet smash) in the fourth set," Zverev said.

Women's fifth seed Karolina Pliskova, whose win over Williams at the US Open ended her 186-week stint as world number one, smashed Spain's Sara Sorribes Tormo 6-2, 6-0.

And Britain's Jo Konta, riding high after her victory at last week's Sydney International, beat experienced Belgian Kirsten Flipkens 7-5, 6-2 to reach the second round.