The fourth and final day of round robin play began with Maria Sharapova facing alternate Sam Stosur.
Samantha Stosur had won two of their last three meetings, though Maria Sharapova led overall, 10-2.
And among the thousands of Turkish fans in the crowd were some Russian supporters of Maria Sharapova.
Maria Sharapova won the first six games of the match and the last four games for a 60 63 victory.
Agnieszka Radwanska prepared for her match with Sara Errani - little did she know what was to come...
Sara Errani was ready for the grind, beginning with taking the first set and going up 2-0 second set.
Agnieszka Radwanska had to dig deep and she did, winning six straight games mid-way through the match.
Agnieszka Radwanska's serve was particularly solid - she hit three double faults in 118 service points.
The six games in a row put Agnieszka Radwanska up 3-0 in the third set and she would hold on, 67(6) 75 64.
The three-hour, 29-minute victory was the longest best of three set match in WTA Championships history.
Sara Errani fell to 0-23 against Top 5 players but is too close not to break the pattern in 2013.
Agnieszka Radwanska, who advanced to the semifinals with the win, posed for a photo with ballkids.
Victoria Azarenka came from 4-2 down in the first set to beat Li Na and reach the semifinals, 76(4) 63.
By virtue of the win, Victoria Azarenka not only made the semis, she clinched year-end World No.1.
A familiar face in the commentary booth - former Top 10 player Alicia Molik alongside Kevin Skinner.