Defending WTA Finals champion Agnieszka Radwanska comfortably beat Karolina Pliskova 7-5 6-3 in a straight shoot-out for the last semi-final spot.

Both players recovered from defeats in their opening matches by winning their second outing in Red Group, setting the stage for a winner-takes-all clash on Friday.

And it was Radwanska who triumphed, the Pole maintaining her 100 per cent record against Pliskova by coming out on top without dropping a set for the seventh match against the Czech in succession to set up a semi-final clash with world number one Angelique Kerber.

With so much on the line neither player wanted to let anything slip in their early service games, but Pliskova eked out a 4-2 advantage.

Radwanska fought back, defending well and impressing when moving towards the net before claiming the first set with an exceptional forehand return.

The Pole moved a break up at the first attempt in the second set but dropped her next two service games to trail 3-2.

However, Pliskova, paying the price for copious errors, capitulated and failed to convert what proved a pivotal break point in game seven, with Radwanska marching on to a semi-final with top seed Kerber on Saturday.

STATISTICAL BREAKDOWN

Radwanska [2] bt Pliskova [4] 7-5 6-3

WINNERS/UNFORCED ERRORS
Radwanska - 15/8
Pliskova - 27/29

ACES
Radwanska - 2
Pliskova - 6

BREAK POINTS WON
Radwanska - 5/8
Pliskova - 3/7

FIRST SERVE PERCENTAGE
Radwanska - 59
Pliskova - 52

PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Radwanska - 74/42
Pliskova - 70/36

TOTAL POINTS
Radwanska - 63
Pliskova - 53