Second seed Radwanska was sloppy in the first set and paid the price as Kuznetsova found 11 winners and broke her opponent twice.

The momentum swung dramatically in the second as Radwanska broke three times and reeled off four games in a row as her net game came to the fore.

Kuznetsova took the unusual move of taking a pair of scissors and cutting around an inch of hair from her ponytail during a third set changeover.

She broke Radwanska in the very next game but surrendered her own serve next up and at 5-4 down successfully bounced back from match point to tie the scores.

The Russian claimed the next two games to secure the win and kick off her finals campaign with a big scalp.

The day's other match in the White Group followed a similar pattern as Karolina Pliskova beat Garbine Muguruza 6-2 6-7 (4/7) 7-5.

The Czech, in her first ever appearance at the season finals, broke twice in succession to lead 4-1 in the first set, eventually closing it out 6-2 with an emphatic unreturned serve.

She also picked off Muguruza's serve in the first game of the second set but the Spaniard levelled at 3-3 and broke to lead 5-3, only to immediately let that advantage slip away.

They went to a tie-break where momentum continued to swing, Pliskova moving 3/0 up and then 4/3 down before Muguruza closed out a 7/4 success.

Pliskova faced match point at 5-2 down in the deciding set on Muguruza's serve but dug deep for two successive breaks to level at 5-5 and a third to clinch victory.