Now the all-conquering world No 1 isn't ruling out crowning her extraordinary comeback from a life-threatening illness with a rare calendar-year Grand Slam sweep in 2015.

As she savoured a record sixth Australian Open triumph, a feat that elevated the 33-year-old above fellow American greats Martina Navratilova and Chris Evert on the all-time major leaderboard, Williams on Sunday recalled her darkest days in 2011.

Williams spent almost 12 months laid up after slashing her foot celebrating her 2010 Wimbledon triumph and then suffering a pulmonary embolism.

The clot on her lungs had Williams on her "death bed", as she put it.

"I didn't think I'd ever be back on court. I really didn't," Williams said after a 6-3 7-6 (7-5) victory over Maria Sharapova earned her a 19th grand slam title.

"I was in the hospital thinking: 'Am I going to make it out?'

"Then I remember asking the doctor: 'Am I going to be able to play tennis again', you know, because it was my career."

In an incredible renaissance, Williams has now won six of the past 13 majors since her ordeal - and since turning 30.

But the oldest Australian Open winner in professional tennis history believes "30 is the new 20" and, while she can envisage a life "on the beach or a boat", the ageless champion says "right now that seems a little far away".

"With technology and stuff, players are able to play longer and I can play as long as I want to," Williams said.

"It just depends on how long I want to. I really don't know.

"I do know I'm having fun. I love winning championships, I love holding trophies up at the end of the week and, more than anything, I love to do the work to get there.

"So when that stops, I'll know I've probably had enough.

"[But] I want to keep winning. The last thing I want is for this to be it."

Having left Navratilova and Evert in her wake, Williams now trails only Australian Margaret Smith Court's all-time record 24 career majors and Steffi Graf's open-era benchmark haul of 22 grand slam singles titles.

The French Open is her next target and, as reticent as she is to publicly talk up her chances, Williams refuses to dismiss the possibility of winning all four majors in 2015, a scenario that would have the US superstar level with Graf by the end of the season.

"I've had an opportunity five times to do a career Grand Slam and I've never done that," said Williams, who achieved the so-called "Serena Slam" in 2002-03 by holding all four grand slam trophies simultaneously but not the same year.

"I don't know, I'm not going to say it's not going to happen, but I'm not putting it out there right now." AAP