Ana Ivanovic, Sam Stosur, Anastasia Pavlyuchenkova and Simona Halep qualified for the semi-finals of the Tournament of Champions in Sofia.
Ana Ivanovic battled past Sam Stosur to maintain her 100% record at the Tournament of Champions in Sofia.
Sam Stosur got her Tournament of Champions off to a winning start against Elena Vesnina in Sofia.
Twice winner Ana Ivanovic started her Tournament of Champions campaign with an easy win over Tsvetana Pironkova in Sofia.
The paths to the US Open women's semi-finals to be played on Friday at the US National Tennis Center in Flushing Meadows.
Victoria Azarenka overcame Alize Cornet 6-7(2) 6-3 6-2 to progress to the last 16 at the US Open.
Order of play for day six of the US Open, with Rafael Nadal, Roger Federer, Victoria Azarenka and Dan Evans on court.
Victoria Azarenka charged into the third round of the US Open with a 6-3 6-1 win over Canada's Aleksandra Wozniak.
Order of play for day four of the US Open, with Rafa Nadal, Roger Federer, Serena Williams and Victoria Azarenka all on court.
Ana Ivanovic made a strong start at the US Open but was playing with a heavy heart after the death of a childhood friend.
Organisers have announced the seedings for the US Open and Roger Federer is seeded only seventh.
Round-up: Serena Williams fought back from a set down to beat Eugenie Bouchard 4-6 6-2 6-2 in Cincinnati.
ATP World Tour Finals
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