A rampant Caroline Wozniacki stunned world number one Simona Halep in straight sets as she stormed into the last four at the WTA Finals on Wednesday.
The 27-year-old Dane broke Halep five times to win 6-0, 6-2 in just 63 minutes at the Singapore Indoor Stadium in the Red Group round robin.
Sixth seed Wozniacki also crushed Elina Svitolina in her opening match in Singapore, winning the last 10 games en route to a 6-2, 6-0 victory.
That tally became 17 games in a row as Wozniacki, looking focused and determined, won the first seven against Halep, whose hold on the top ranking looks increasingly shaky.
Wozniacki, a former world number one, broke three times in an almost flawless first set, in which she served at 94 percent and made just two unforced errors.
She barely let up in the second set as she continued to masterfully move the flummoxed Halep around the court, hitting the lines with precision.
Halep finally got on the board early in the second set but she was broken in the fourth game and then again on match point, capitulating with a meek forehand into the net.
Wozniacki is one of seven players in the eight-woman field who could finish the year as world number one by lifting the trophy on Sunday.
It was a bitterly disappointing evening for Halep, who only became world number one earlier this month, and who was impressive in her opening victory over Caroline Garcia.
The 26-year-old now finds herself in a battle to reach the semi-finals, and next plays Svitolina in a crunch match on Friday.