
Serena Williams battled her way to three grand slams in 2015 to lift her total to 21, one shy of the Open Era record set by Steffi Graf.

She was only foiled in her bid to achieve the calendar year grand slam by Roberta Vinci at the U.S. Open in September.

But is Williams healthy ahead of the Australian Open? She retired from her opening match at the Hopman Cup and then withdrew from the Perth warmup event with a knee complaint.

Men's No. 1 Novak Djokovic has no such issues, although the Serb admitted his arm bothered him at a tournament in Doha last week. Djokovic won three majors in 2015 and also the year-end championships in London.

He has won 45 of his his last 51 matches against top-10 players, including going 31-5 in 2015.

Djokovic thumped Nadal in the 2016 Doha final, and last year the Spaniard failed to win a major for the first time since 2004.

But the end of the season was much better for the 14-time grand slam champion, who reached finals in Beijing and Basel while making the semis at the ATP World Tour Finals.

If you're looking for the second favorite to Williams -- she may even be the favorite -- Victoria Azarenka could be the pick. The two-time Melbourne champion has recovered from a foot injury and won a warmup in Brisbane in convincing fashion.

Is this Andy Murray's year to break through in Melbourne? He's been to the final four times -- losing three of them to Djokovic, including 12 months ago.

Murray's wife Kim Sears is pregnant with their first child, and the world No. 2 says he will fly home to the UK if she gives birth during the tournament.