Kerber, the winner of the Australian Open and US Open, had virtually guaranteed her spot in the last four by winning her first two contests and she completed her 100 per cent record by beating Madison Keys of the United States 6-3, 6-3.

Cibulková had earlier overcome Romania's Simona Halep 6-3, 7-6 - her first win of the week - but she needed Kerber to clinch a straight-sets triumph in order to progress to the semi-finals at the expense of the American.

Her success ensured Kerber’s semi-final berth and she required the German to return the favour.

Thankfully for the Slovakian, seeded seventh at the season-ending event, the top seed duly obliged to ensure she prolonged her stay in the tournament in Singapore.

Cibulková, whose best Grand Slam result came when she finished as runner-up at the 2014 Australian Open, will take on Russia’s Svetlana Kuznetsova in the last four.

The Russian only secured her spot at the WTA Finals - which features the top eight available female players in the world rankings - on Saturday (October 22) when she won the Kremlin Cup on home soil in Moscow.

The two-time Grand Slam winner, who is enjoying a resurgence in the twilight of her career, became the first player to reach the semi-finals yesterday.

"They call me the fighter and there’s a reason for it – I showed it today," Cibulková said.

"It wasn't easy to go on court today after two losses.

"I didn’t win a match until today and I really wanted it.

"I knew I had to win in two sets to have a chance to go to the semi-finals so I was really fighting for the [second] set."

Kerber will face the victor of tomorrow’s crucial white group clash between defending champion Agnieszka Radwanska of Poland and Karolína Plíšková of the Czech Republic.