Australian tennis champion Sam Stosur reached the pinnacle of her career in 2011 when she dethroned former Serena Williams to take the US Open crown - and she has revealed she was almost certain she'd win the night before the match.

On Saturday, Stosur announced via Instagram that this year's Australian Open will be her last professional tournament.

The 38-year-old also won seven mixed doubles and women's major titles, but it was her underdog straight sets victory over Williams that she'll remain best known for. 

'I don't know what it was - the night before when I got myself into the final, I just had this feeling I was going to win the next day,' Stosur told Weekend Today on Sunday. 

'I mean, that's a moment that every athlete dreams of … being in the zone. Doing everything that you want to do. For whatever reason it happened that day for me.'

The Queenslander got past Angelique Kerber, Nadia Petrova and Maria Kirilenko to secure a spot in the final before taking out her only singles major - becoming the first Australian woman since Margaret Court in 1973 to triumph at Flushing Meadows.

The former world No.4 was also dominant on the French clay, reaching the final four on four occasions, including a loss in the 2010 decider.

Making her professional debut aged 15 in 1998, Stosur conceded time 'snuck up on her' before she announced her retirement in an emotional social media post on Saturday night.

'I'm really grateful for this past year, but now I get to do normal things at home - I'll probably be the one doing childcare drop off or something like that,' she said.

Stosur will be looking to emulate her 2005 Australian Open success where she won the mixed doubles with fellow Aussie Scott Draper.

The two defeated Liezel Huber and Kevin Ullyett in the final 6–2, 2–6, [10–6].

Stosur rose to a career-best world No.4 singles and No.1 doubles ranking during the 2000s.

Aussie Matt Ebden will partner Stosur in the mixed format this year while France's Alize Cornet joins the veteran in the women's doubles. 

'Even though I've made the decision to retire from the sport I absolutely love, a small part of me would be happy to keep playing forever,' Stosur wrote on Instagram.

'I feel so happy and grateful to have the opportunity to finish playing at my favourite slam – my home slam – in front of my Aussie fans, friends and family.'