Whenever Williams steps out on court, the 21-time grand-slam champion has an obligation to deliver win after win, trophy after trophy.

And it was no different in Saturday's Australian Open decider, which she lost 6-4 3-6 6-4 to seventh seed and slam-final debutant Angelique Kerber.

Fans watched on in disbelief as six-time champion Williams - who lost her first Australian Open final in seven appearances - struggled to find her range in the opening set, tallying a staggering 23 unforced errors.

She finished with 46.

To put things in perspective, the world number one only managed 17 in the semi-finals against Agnieszka Radwanska.

Her tournament-high was 22.

Williams, who had limited preparation for the Australian Open due to a knee problem, admitted to pre-match nerves on Rod Laver Arena and they were probably for good reason.

After missing out on the calendar Grand Slam following last year's surprise semi-final exit at the US Open, all eyes were on the 34-year-old in her quest to match Steffi Graf's achievement of 22 majors and close in on record-holder Margaret Court (24).

But Williams fell short of expectations, again.

"Every time I walk in this room, everyone expects me to win every single match, every single day of my life. As much as I would like to be a robot, I'm not. I try to," Williams said after her three-set loss to Kerber.

"But I do the best that I can. I try to win every single time I step out there, every single point, but realistically I can't do it. Maybe someone else can, but I wasn't able to do it."

Williams did go through a difficult patch in 2014, failing to make it past the fourth round at the Australian and French Opens, as well as Wimbledon before taking out the US Open.

And with three majors still on offer in 2016, Williams could well catch Court by the end of the year.

But on the wrong side of 30 and with her body showing signs of wear and tear, Williams is proving she is no robot.