Caroline Wozniacki ensured she would end the year as the world number one after defeating French Open champion Francesca Schiavone at the WTA Championships last night.

The 20-year-old Dane reached the top ranking for the first time in her career earlier this month and ensured she would hold onto it at season’s end with her 3-6 6-1 6-1 win over Schiavone.

The victory also ensured Wozniacki would join Sam Stosur, who beat her on Wednesday, in the semi-finals of the end-of-season tournament.

“This has been the most amazing year in my career during which I realised my dream of becoming world number one,” Wozniacki said.

“Capturing the year-end world number one ranking is a huge accomplishment for me and I am thrilled that all the hard work has paid off.”

Fifth seed Stosur earlier booked her place in the last four despite losing to Elena Dementieva 4-6 6-4 7-6 (7/4).

The Australian won her opening two matches against Schiavone and Wozniacki to ensure the set she picked up was at least enough to send her through.

For Dementieva it was a morale-boosting win after she had been a set and a break behind.

“It wasn’t easy to play today after losing to Caroline very easily, but I just tried to improve and be ready for today,” the Russian said.

“Sam had a great win last night. I tried to fight for every point. I’m really enjoying my time here, it’s very special for me to be here in Doha playing the WTA Championships.”