With the win, Halep takes over as number one in the world.
A blockbuster first-round clash in NY went the way of Sharapova but Halep produced a brilliant performance in Beijing to win 6-2 6-2.
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. Ostapenko had a chance to pull it back in game 6 but her backhand hit the top of the net and landed long, and Halep moved 4-2 ahead after 23 minutes.
Halep, who is coached by Australia Darren Cahill, has repeatedly missed out this season on the top spot while standing just one win away from ranking glory.
"I was injured and I didn't believe I would even be in Singapore. It's my first victory against her and I just want to enjoy the moment". "I changed the tactic and worked pretty well".
"It's very emotional, I think it's the first time I cried on court", Halep said on-court after the match.
Wuhan Open champion Caroline Garcia of France overcame Belgian Elise Mertens 7-6 (4) 6-4, while Ukrainian Elina Svitolina beat Australia's Ashleigh Barty 6-4 6-2 in the second round to set up a clash with Russia's Elena Vesnina.
The outstanding Williams is temporarily out of tennis after having her first child. A solid first set won by 6-2 put the second seed in front.
A year ago the 22-year-old was suspended by tennis authorities for his behaviour in a defeat in Shanghai during which he appeared to give up and argued with the crowd. Still, she played really well those games, those next games [after falling 3-2 down].
Kyrgios's exuberance won favour with the crowd in the Chinese capital and after winning one thrilling rally he turned to the spectators and gestured with flailing arms for them to keep roaring him on.