She is the newly crowned world No. 1, as well as the player who has amassed the most points on tour this year. Yet, by Simona Halep's own admission while the match was ongoing yesterday, the mission seemed nothing but "impossible".

Such was the confidence and precision that her opponent played with, as Caroline Wozniacki claimed a swift 6-0, 6-2 victory. It was the Dane's second straight win in the group stage of the BNP Paribas WTA Finals Singapore presented by SC Global, both matches equally one-sided.

Halep, keen to replicate the good practice session she had before her match yesterday, said she struggled to deliver shots of a similar quality.

So even as coach Darren Cahill came on court during a changeover, urging his charge to stay in the points, she agreed in her mind but found herself unable to execute the instructions. "I couldn't feel the ball. I didn't feel it," said the 26-year-old yesterday. "I felt everything slow, and I wanted to overhit the ball."

As a result, far too many unforced errors leaked from her racket - 17 to Wozniacki's seven in a match that took just over an hour.

Up against an opponent who leads the women's tour for the most match wins this season and is a former world No. 1 herself - Wozniacki held the ranking for 67 weeks - it meant a helpless Halep.

Said the Romanian, playing in her first tournament as the world's top-ranked player: "I knew that her game is just to keep playing, to put you in a (difficult spot), but also, I knew that I have a chance against her because I won many times on hard (court)."

Wozniacki had led their head-to-head 3-2 prior to yesterday but both of Halep's wins had come on hard courts. Said Halep: "It was one of my bad days. I made too many mistakes and she (Wozniacki) didn't miss."

Wozniacki's deep and aggressive ground strokes yesterday, coupled with her signature defensive play, made her the first player from the Red Group to earn a place in the final four. She joins Czech Karolina Pliskova from the White Group.

Little, if anything, felt out of sorts yesterday for Wozniacki, who converted five of her eight break points. She said: "I just ran a lot of balls down, I played (aggressively), and I mixed up the pace, and everything that I wanted to do kind of was going my way."

With a perfect 3-0 record in the group stage the last time she competed in 2014, Wozniacki has both the track record and the current form to run deep this year. She said: "You come into the tournament knowing that you can easily go 0-3 in the group. I think that kind of motivates me to just start off strong and just go for it."

She is through to the semi-finals with Halep, Elina Svitolina of Ukraine and Caroline Garcia of France vying for the remaining spot.

In danger of being eliminated if she had lost her match yesterday, Garcia came from behind to beat Svitolina 6-7 (7-9), 6-3, 7-5. Said Garcia, who was the last player to qualify for this tournament: "When I was down, I kept believing. You work so hard outside of the court, every thing happened so quickly and I was very stressed to be here, but now I'm enjoying it."