Halep ensured she would replace Spaniard Garbiñe Muguruza, who retired ill from the tournament earlier this week, at the summit of the rankings with a 6-2, 6-4 win over Ostapenko at the Olympic Green Tennis Center.

The victory avenged her shock defeat to the Latvian in the semi-finals of the French Open earlier this year.

The 26-year-old will be confirmed as the world number one for the first time when the updated rankings list will be published on Monday (October 9), following the conclusion of the event in the Chinese capital tomorrow.

"It was the toughest year but also the best year," said Halep.

"At the beginning, it was very tough. 

"I was injured and I didn't believe I would even be in Singapore. 

"So being there now and being number one today, it's great.

"I just enjoy the moment and take the very happy moments that I had this year."

Caroline Garcia will be Halep's opponent in the final after the Frenchwoman overcame 12th seed and double Wimbledon champion Petra Kvitová of the Czech Republic 6-3, 7-5.

Garcia took the opening set before Kvitová fought back in the second.

The Czech player, who made her return from a hand injury she suffered when she was stabbed in a knife attack at her home in December at the French Open, led 5-3 but Garcia claimed four straight games to reach the final.

In the men's tournament, top seed Rafael Nadal battled past Bulgarian Grigor Dmitrov in three sets in a gruelling semi-final encounter.

The Spaniard, a 14-time Grand Slam champion, progressed by virtue of a 6-3, 4-6, 6-1 triumph over the third seed.

He will meet either Australian Nick Kyrgios, who stunned second seed Alexander Zverev of Germany 6-3, 7-5.