SAMANTHA Stosur’s long reign as queen of Australian tennis is under threat after a dismal finish to her 2016 season.

Stosur crashed out of the Elite Trophy round-robin event in China with successive straight-set defeats, leaving the one-time grand slam champion and world No.4 winless since the US Open in late August.

The 32-year-old’s slide has coincided with her split from long-time mentor David Taylor following her charge to the French Open semi-finals in June.

Working with a third new coach in four months, Stosur has won only six of 14 matches since and lost her past five in Asia without managing a set.

After a two-title haul in 2015, Stosur failed to land a trophy this season for the first time in four years and will head into the Australian summer with her Australian No.1 ranking under siege from rising star Daria Gavrilova.

In contrast to Stosur’s none-from-five record, Gavrilova chalked up 10 wins during a hugely successfully Asian swing, with runs to the quarter-finals in Beijing, semis in Hong Kong - where she beat world No.1 Angelique Kerber - and the final in Moscow slashing the 22-year-old’s ranking in half.

Stosur has held the Australian top ranking for more than seven years, but is set to end 2016 just three spots above Gavrilova at No.21 in the world.

While Gavrilova has fourth-round rankings points to defend at the Australian Open, where Stosur bombed out in her opener last year, Stosur made the quarter- finals in Sydney and will be under pressure to at least repeat that effort.

Stosur has traditionally struggled to perform in front of home fans but, turning 33 in March, she and new coach Josh Eagle will need to quickly reverse the veteran’s fortunes to prevent a changing of the guard.