Towel draped over her head, down a set and trailing 1-4 midway through the second, three words kept replaying inside Simona Halep's head.

"I was telling myself that I was done," admitted the world No. 2 afterwards as she reflected on her 6-7 (5-7), 1-6 loss yesterday to Agnieszka Radwanska, which also ended the Romanian's participation in the BNP Paribas WTA Finals Singapore presented by SC Global.

A losing finalist in last year's edition, Halep finished third in the Red group and became the first top seed since Caroline Wozniacki in 2011 to exit the season finale at the round-robin stage.

Yet the US$7 million (S$9.75 million) tournament had started so promising for Halep, whose game brimmed with energy and aggression when she routed Flavia Pennetta in the opening match on Sunday.

A straight-set loss to Maria Sharapova on Tuesday halted her momentum but against Radwanska, Halep seemed to have rediscovered her mojo as she dictated from the baseline and broke the world No. 6 in the opening game at the Singapore Indoor Stadium.

The Pole recovered to level in the sixth game but was struggling with her service games even as Halep failed to convert any of her six break-point opportunities.

With a 5-1 lead in the tie-break though, there seemed little chance that Halep would let another chance slip away.

But Radwanska, who has bageled Halep twice in their eight previous encounters (tied at 4-4 before yesterday), refused to surrender.

Instead she reeled off the next six points - highlighted by two audacious overhead backhanded volleys - to knock a stunned Halep off her feet even as the fans rose to theirs to salute Radwanska.

Having nothing to lose gave her the freedom to take more risks, said Radwanska. "I didn't get tight and I think I made really good shots in important moments. At 5-1 down I just kind of play aggressive tennis and that works.

"I was pretty relaxed, still fighting, still playing. When you really relaxed I think sometimes it's better."

She hit 21 winners and won almost 50 per cent of points in rallies of more than five shots, the most she has managed in both categories all week.

The psychological impact of that tense 74-minute battle proved telling, as Halep was broken thrice with the second set (45 minutes faster than the first) going by in a blur.

Halep has three hard-court titles and more wins (41) than anyone else on the surface this term but has struggled recently with an Achilles injury.

She said: "I had no energy. I was tired. I felt that I lost the chance to win the first set (in the tie-break) and probably I lost the chance to win the match in that moment.

"My coach was telling me many things but I couldn't hear because I was done and I was very nervous there."

After two earlier losses - coincidentally, Radwanska also qualified for last year's semis after suffering two losses in the group stage - her first victory in this year's event was especially sweet.

Not only was it her 500th career WTA win, it also secured her a spot in the semis after Sharapova maintained her perfect group record by beating Pennetta 7-5, 6-1 later.

Said Sharapova, the 2004 Finals champion: "Every match for me counts. I wanted to play three high- quality matches but also I'm a bit surprised I managed to win all three."

While US Open champion Pennetta prepares for the business end of the competition, this was the final chapter for her, as she needed to win a set to hold off her retirement at least until the weekend.

Meanwhile, for someone whose dream vacation is on an sunny island with sandy beaches, a prolonged stay in the Republic for work may not count as a holiday, but Radwanska will not mind one bit. After all, she is not yet done in Singapore.

ROUND ROBIN

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