Singapore, Oct 25 (IANS): After three sets of fierce competition with good friend Caroline Wozniacki, top seed Serena Williams managed to qualify for the WTA Championships final to be held Sunday.

She will again compete with Simona Halep, who gave the American an ugly 0-6, 2-6 defeat during the round robin Wednesday, reports Xinhua.

It was not a good start for Williams. Wozniacki, who qualified for the semi-finals with all wins during round robin, got the first breakpoint and led the game 3-0. The Polish girl maintained the lead in the first set, finishing it 6-2.

Both of them held serves at the beginning of the second set, before Williams, who successfully broke at the third point, started to fight back. The World No.1 threw herself into the race in full force and ended up winning the second set 6-3.

Audiences were treated to another ferocious battle during the final set where Wozniacki first took the opportunity and led the game at 5-4. However, she failed to maintain the momentum and Williams dragged the game into tiebreak to overtake her rival 7-6.

However, Williams was not satisfied with her performance.

"Why am I starting out so flat? I had a good warm up and I wanted to have a really good start but it just wasn't happening. I need to figure that out actually because it's inexcusable for it to happen once, let alone twice," she said.

Meanwhile Halep crushed Agnieszka Radwanska with two 6-2s in the other semi-final.

Williams made it clear that she won't allow what happened to her Wednesday. "I don't want a repeat of the other day so my whole goal was just to not lose 6-0."