Agnieszka Radwanska came through a three-set marathon with Sara Errani to earn a semi-final meeting with Serena Williams at the WTA Championships in Istanbul.
Radwandska needed just under three-and-a-half hours to prevail 6-7 7-5 6-4 in a match that was a straight shoot-out for second place behind Maria Sharapova in the White Group.
The opening set featured 10 breaks of serve, five for each player, followed by a tie-break that Errani eventually claimed 8-6.
Radwanska twice surrendered her own delivery immediately after breaking in the second set and then found herself 5-4 down and serving to stay in the tournament.
The Pole responded in style, reeling off 12 unanswered points to take the next three games and force a deciding set.
And Radwanska continued her dominance at the start of the third set, moving 5-2 up before serving out victory at the second time of asking.
Her reward is a meeting with Williams, who topped the Red Group with a 100 per cent record.
Radwanska said: "First of all I will have a lot of treatment just to stay in one piece. Serena is a great champion and in that kind of match I have nothing to lose."
Victoria Azarenka and Li Na meet in the final match of the Red Group to determine who will advance to play Maria Sharapova in the other semi-final. Sharapova, like Williams, won all three of her matches in the round-robin phase.