Elina Svitolina produced one of the best performances of her career to overcome defending champion Caroline Wozniacki 5-7, 7-5, 6-3 in a pulsating round robin encounter and reach the last four of the WTA Finals with a spotless 3-0 record on Thursday.
Earlier in the day, Karolina Pliskova became the first woman to advance when the big-hitting Czech curbed her attacking instincts to beat compatriot Petra Kvitova 6-3, 6-4 and record her second win against a single loss in White Group play.
By winning her opening two matches, Svitolina only needed to take one set off the Danish world number three to advance and after playing so brilliantly all week, the Ukrainian proved equal to the task.
"It was an amazing match as Caroline always brings the best out of you, to really push yourself, so I have to thank her for making me push my limits," Svitolina said in a post-match interview after handing Wozniacki her second loss of the week.
"I am more mature now so it was all about staying calm and fighting for every ball."
Wozniacki and Svitolina are both excellent counter-punchers with supreme athletic ability and after trading blows from the baseline at the start of the match, the Dane mixed up her shots brilliantly to forge a set-winning break in the 11th game.
The contest had effectively become a one-set shootout for a semi-final spot and Wozniacki showed the class that swept her to victory in Singapore a year ago and the Australian Open title in January to move ahead with an early break in the second.
Back came Svitolina, however, stepping in from the baseline to take the ball earlier as she broke immediately and the intensity levels threatened to blast through the Singapore Indoor Stadium roof.
Neither player was willing to budge an inch as the set appeared destined for a tiebreak, until Svitolina fashioned five set points in an epic 12th game, sealing her place in the last four when Wozniacki sent a backhand long.
Svitolina celebrated winning the set as if she had won the match, fist-pumping and roaring towards her box, the Ukrainian carrying the momentum forward and needing just a single break of serve in the deciding set to finish top of the group.
Kvitova, meanwhile, had lost her opening two matches and knew that only a straight-sets win would give her any chance of advancing, but Pliskova stayed calm and focused to record a first triumph over her compatriot in four attempts.
The double Wimbledon champion needed to make a fast start to put her opponent under pressure, but Kvitova lacked movement and coughed up a slew of double faults to slip 4-0 behind in the blink of an eye as Pliskova pounced on every opportunity.
Slowly but surely, Kvitova worked her way back into the contest, rallying twice from 40-0 down to win back-to-back games in the middle of the set that finally gave Pliskova something to think about.
Pliskova's coach Rennae Stubbs urged her to stay disciplined in the next changeover, and the Czech heeded the advice to curb her attacking instincts as she ended Kvitova's tournament by holding serve to take the opener in 41 minutes.
The loss of the opening set appeared to free up Kvitova's booming forehand and she feasted on Pliskova's tentative start to the second set to race to a 3-0 lead, but the world number eight battled back brilliantly to book her semi-final place.
"I cannot be more happy right now. It was a good match and she's a great player. She has always beaten me in the past but I knew I had a chance as I have been playing well," Pliskova said in a post-match interview.
"I'm not thinking about the next match yet, I'll do what I can to recover first. Before the tournament, I said to myself that I want to enjoy it and I will continue to do just that."