Serena Williams delivered an emphatic message about her form and fitness as the American breezed through a fiendish Australian Open first round against Belinda Bencic.

Williams has only played two competitive matches since the US Open in September and many predicted a tough test against Bencic, under-ranked due to injuries at 59 in the world.

The number two seed, however, showed few signs of rust on Rod Laver Arena, dispatching Switzerland's Bencic 6-4 6-3 to advance to round two.

Williams will now face the Czech Lucie Safarova in a repeat of 2015's French Open final, which the 22-time grand slam champion narrowly won in three sets.

After losing in the US Open last four in September, Williams skipped the rest of last year in a bid to overcome a niggling shoulder problem.

Her return in Auckland earlier this month did little to inspire confidence, however, as she was beaten by fellow American Madison Brengle, ranked 72nd in the world.

Bencic has more pedigree, as well as a victory over Williams in their previous meeting in 2015, but she ran into the 35-year-old in defiant mood rather than struggling to rediscover her groove.

Williams hit eight aces - often a strong indicator of her form - and 30 winners, and despite a minor slip-up in the second set, never looked in danger of defeat.

"She was just recently in the top 10 so I knew it would be one of the toughest first-round matches I've ever played," Williams said afterwards.

Williams has played just two matches since September but looked at full fitness on Tuesday (Getty)

"She's a really good player. So I think I was able to start out well. I just wasn't as aggressive at the end as I was during those games.

"She started playing better. I made a few errors on some key points but for the most part, I still was going for everything and I was able to close it out."