Caroline Wozniacki is a good friend.

So good, that she stepped on court on Friday in Singapore not really needing to win but she gave 100 per cent anyway to rout Petra Kvitova, and in the process, allowed her long-time pal Agnieszka Radwanska to secure a spot in the semi-finals.

Friendship will mean little though when Wozniacki takes on another BFF, Serena Williams, who clinched the year-end No1 ranking and booked a place in the semis without picking up a racquet on Friday.

It will be the fourth meeting of the year between the pair and the Dane, who enters the semis undefeated this week, is well aware of her poor record against Williams.

“My matchup against Serena so far hasn’t been great,” said Wozniacki after easing past Kvitova 6-2, 6-3 yesterday.

“I’ve won once and lost nine or ten times. I don’t even count anymore. But it’s a new tournament and it’s a new week. I’ve been playing well really and I believe that if I play like I did today then it doesn’t matter who’s on the other side [of the court], I can win.”

– Sharapova crashes out of Finals despite win

Wozniacki is actually 1-9 against Williams, who was only guaranteed a place in the last four after Romania’s Simona Halep took a set off Ana Ivanovic in the last round robin match of the tournament last night.

Ivanovic had to win in straight sets to make it through to the semis but fell short, ending her season with a WTA-leading 58 wins but not enough to stop Williams from taking second place in the Red Group behind the Romanian.