SHENZHEN, China - For the second time in a month, No.7 seed Belinda Bencic played spoiler to Kiki Bertens, taking the final Red Group round-robin match after the Dutchwoman retired trailing 7-5, 1-0 with a viral illness to seal a coveted semifinal spot at the Shiseido WTA Finals Shenzhen.

"I had some problems with my stomach," Bertens revealed afterwards. "The energy was not there. A little bit dizzy. Just too much to continue... I think I gave absolutely everything this year and this week. I'm proud of that. Like five weeks ago, I said to myself, You're completely dead. I guess now I'm almost there."

The various scenarios in the group had come down to a straightforward winner-takes-all contest: today's victor would finish second behind No.1 seed Ashleigh Barty and move on to face No.8 seed Elina Svitolina in Saturday's semifinals, while the tournament would be over for the loser. Having already denied Bertens a place in the original Shenzhen field by winning Moscow two weeks ago, Bencic denied her again with key tactical adjustments and greater energy to come from a break down in the first set before the alternate's tank ran dry in the second.

"Maybe her gas just really ran out," commented Bencic afterwards. "It was a bit unfortunate. Obviously not the way I wanted to win, but super proud of how I fought in that set. I was thinking maybe she wins the first set, maybe different story. I think after I lost the first match here, I just wanted to keep fighting, and you never know. There's people that made it to the semifinal when they won just one match. I was always thinking of those positives. I think everyone is exhausted and injured, all of that. I think now it's all about the mental strength to go through all of this."

A cagy opening to the match had seen the Swiss player pressure her opponent's serve first - only for Bertens to fend off two break points in the fourth game with her renowned first serve, and to take advantage of a rattled Bencic's errors to immediately get the break herself for 3-2. 

However, serving for the set the 27-year-old wobbled for the first time: having failed to make a significant impact on the Bertens first serve to this point, Bencic began to get returns back in play - and backed them up by bold net approaches.

"I needed to do that," recalled Bencic. "I had no choice because she was really slowing down the pace. Especially on this court - it's good for her and players like her with the slices and with the off-pace shots. I definitely tried to force that and make her more under pressure, go through it, make my shots faster."

The tactical adjustment worked, as did increased sharpness on big points: the Dubai and Moscow champion won each of the last four games of the set to 30 from 3-5 down, with Bertens making key errors on desperate dropshot attempts while Bencic's backhand and drive volleys went from strength to strength.

After a love hold from Bencic to open the second set, Bertens - who was competing for an eighth consecutive week since the US Open - would take a medical timeout, following which she concluded that she was unable to continue, sending WTA Finals debutante Bencic through to face Purple Group winner Svitolina in the last four.