She may have proved that she was human but world No.1 Serena Williams was still at her unstoppable best as she booked a Brisbane International quarterfinal berth on Tuesday.

The 17-time grand slam champion overcame a rare air swing that brought a welcome smile to outclassed German opponent Andrea Petkovic’s face to cruise to a 6-4 6-4 second round win at Pat Rafter Arena.

Williams, 32, cut a frustrated figure after unforced errors as she blew the rust off in her first match of the new season.

But the defending champion did not know how to react when she stormed to the net in the fifth game of the second set for yet another winner, only to completely miss former world No.9 Petkovic’s floating return.

Petkovic – now the world No.43 – had a good natured giggle but there was little else to smile about as Williams extended her overall winning streak to 19 matches.

Williams booked a quarterfinal against Slovakian ninth seed Dominika Cibulkova, who was the first into the final eight when she ousted wily 43-year-old Kimiko Date-Krumm of Japan 6-3 1-6 6-3.

Williams arrived in Brisbane to kick start a bid to back up her 2013 heroics – but that will be easier said than done.

Finishing the year with 11 titles and more than $12 million in prizemoney, Williams’ French and US Open triumphs took her grand slam total to 17, one shy of Chris Evert and Martina Navratilova and just five away from Steffi Graf’s open-era record of 22.

And her 2013 match record stood at 78-4.

Williams is eyeing her 58th career title in Brisbane.

In contrast, Petkovic, 26, is trying to regain her mojo.

The three-time grand slam quarterfinalist is still battling her way up the world rankings after a wretched 2012 in which she withdrew from the 2012 Australian Open with a back complaint, sidelining her until April, before suffering a serious knee injury at the Hopman Cup in December the same year.

As a result, her ranking dropped as low as No.177 in March before fighting back to No.43 this year.

Meanwhile, former world No.1 Jelena Jankovic crushed Ukraine’s Elina Svitolina 6-1 6-3 to cruise into the Brisbane International quarterfinals on Tuesday.

The Serbian fourth seed made short work of world No.45 Svitolina – ranked 37 places lower than Jankovic.

The 28-year-old Jankovic remains on track for a semi-final showdown with world No.2 Victoria Azarenka.