Angelique Kerber is on the brink of reaching the last four of the WTA Finals after the world number one beat Simona Halep in straight sets on Tuesday.
The Australian and US Open champion started the tournament with a victory over Dominika Cibulkova and downed third seed Halep 6-4 6-2 in Singapore two days later.
Top seed Kerber will be through to the semi-finals if Cibulkova gets the better of Madison Keys in the other Red Group game later in the day, while Halep can still advance with one round-robin match against the Slovakian to come.
Kerber needed three sets to get the better of Cibulkova on day one of the season-ending event and looked in no mood to hang around as she broke in the first game of the match.
Halep responded with some classy ground strokes and broke back to leave at 3-3 after Kerber lost her way, but the Romanian paid the price for too many errors to enable the favourite to regain her grip on the match.
The Olympic silver medallist wrapped up the set by winning three games in a row and wound up her forehand to put Halep on the back foot, also having joy with the drop shot that has served her so well this year.
Halep, a runner-up in this competition two years ago, was unable to turn the tide as a fired up Kerber breezed into a 5-1 lead and levelled their head-to-head record at 4-4 with a fourth victory in five matches between the two in what has been a stellar year for the German.
Kerber  bt Halep  6-4 6-2
Kerber - 11/16
Halep - 24/35
Kerber - 0
Halep - 1
BREAK POINTS WON
Kerber - 4/5
Halep - 1/6
FIRST SERVE PERCENTAGE
Kerber - 55
Halep - 63
PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Kerber - 70/48
Halep - 56/45
Kerber - 70
Halep - 57