The American has not lost in Melbourne since being stunned by Jelena Jankovic in the 2008 quarter-finals. Yet she comes into the tournament as the 12th seed and with questions surrounding her fitness - she missed last year's event with a foot injury and the subsequent discovery of a blood clot on the lung gave her another sizeable hurdle to overcome.
But on the evidence of the first week she remains the woman to beat.
Williams was far too good for Greta Arn in their third-round clash, easing to a 6-1 6-1 win in under an hour.
The 13-time grand slam champion has dropped just 11 games in reaching the fourth round but believes there is more to come.
"I can hit a little deeper and better, be more consistent," she said.
"Hopefully that will come as I keep playing."
Given her lack of match practice, Williams could have been forgiven for feeling under-cooked heading into week two but she is quite happy with how things are progressing.
"I'm pretty experienced so I kind of know what the feeling of having tough matches is, and having simple matches is, so it's okay," she added.