Williams is playing for the first time since her historic return to the No.1 ranking - on February 18, after reaching the final of another Premier event in Doha, the 31-year-old Williams became the oldest No.1 in the history of the WTA. Seeded No.1 this fortnight, she - like every other seed - received a first round bye, and will begin against either Flavia Pennetta or Johanna Larsson in the second round.
This has been one of Williams' very best tournaments, winning it five times before in 2002, 2003, 2004, 2007 and 2008. The tournament has been running since 1985 and only one other player has won that many titles, namely Steffi Graf, who also won it five times in 1987, 1988, 1994, 1995 and 1996.
Another player making an even longer-awaited return to action is Li Na, won won 14 of 16 matches in the Australian season and moved back into the Top 5 afterwards - but subsequently had to pull out of all of her scheduled tournaments since due to a left ankle injury. But she's back and is the No.5 seed here, in Williams' quarter too - she opens up against either Kiki Bertens or Anna Tatishvili.
Azarenka, the No.2 seed, has had fantastic results here before, winning the title twice in 2009 and 2011, and although she had to withdraw from her quarterfinal match at Indian Wells last week with an ankle injury, she is still an unbeaten and intimidating 17-0 on the year. She will open against Madison Keys or a qualifier, and the other Top 8 seed in her quarter is No.6 seed Angelique Kerber.
Sharapova, the No.3 seed, is coming off her first WTA title of the year at Indian Wells, and though she has never won in Miami, she is a four-time finalist. Fresh off a return to the No.2 ranking - the seedings for Miami were set before that ranking shift - the new World No.2 begins against either Eugenie Bouchard or a qualifier. The other Top 8 seed in her quarter is No.8 seed Sara Errani.
Radwanska, the No.4 seed, went 13-0 to start the season but has cooled off a little bit since then, going 6-4 in her last 10 matches - but these courts have inspired great things from the Polish star in the past, as she won the biggest WTA title of her career here a year ago. She opens against Hsieh Su-Wei or Lesia Tsurenko and if things hold to form would face No.7 seed Petra Kvitova in the quarterfinals.
Williams, Azarenka and Radwanska aren't the only former Sony Open Tennis champions in the draw. Venus Williams, the No.19 seed, won here three times in 1998, 1999 and 2001, and is in Radwanska's section of the draw; Svetlana Kuznetsova, who won here in 2006, is in Errani's section of the draw.