Star Indian shuttlers P V Sindhu and Kidambi Srikanth fought their hearts out before suffering close defeats in their respective Group B opener at the $1.5 million HSBC BWF World Tour Finals here on Wednesday.

A week after a demoralising defeat at the Toyota Thailand Open quarterfinals, world champion Sindhu produced a much-improved performance but still lost to world No. 1 Tai Tzu Ying of Taiwan 21-19, 12-21, 17-21.

"It was a good match, there were no easy points. In the third game I came back and it was just one point difference at one stage. I broke my racket strings twice (during rallies) and that made a difference," Sindhu said.

"It's a tough group. I have to give 100 per cent."

It was Sindhu's 16th defeat to Tzu Ying in 21 meetings.

Former world No. 1 Srikanth too squandered an opening game advantage, losing 21-15, 16-21, 18-21 to world No. 3 Anders Antonsen of Denmark in a gruelling 77-minute contest.

Olympic silver medallist Sindhu, who had won the prestigious title in 2018, will next play home favourite Ratchanok Intanon, who had handed her a humiliating defeat last week, while Srikanth, ranked 14th, will face fourth seed Wang Tzu Wei of Chinese Taipei on Thursday.

The opening game was a close fight as Sindhu and Tzu Ying engaged in an enticing battle.

Tzu Ying led 5-3 early on before grabbing an 11-8 advantage at the interval as Sindhu lost a few points on the net.

After the break, Tzu Ying jumped to a 14-10 lead with Sindhu making an error in her judgement at backline and also the Taiwanese producing a backhand cross court return.

Sindhu drew parity at 16-16 with a run of points, highlighted by a crisp cross court slice and a backhand return.

Tzu Ying again moved ahead but two precise smashes helped the Indian make it 19-19 as she grabbed the game point with another precise return that kissed the backline.

Sindhu then played a cross court return at the net which her opponent couldn't reach, gaining the upper hand in the match.

Tzu Ying zoomed to a 6-0 lead in the second game. Sindhu managed to reduce the deficit to 3-7 before the Taiwanese unleased a couple of drops and a smash to make it 9-4.

Two unforced errors from Sindhu handed an 11-4 advantage to her rival at the break. Tzu Ying continued to dominate to move to 19-9 before winning the second game with a cross court return.

In the decider, Tzu Ying again led 6-3 but she stumbled to defensive errors as Sindhu levelled the score with a smash.

However, the second seed Taiwanese held an 11-9 lead at the break after Sindhu made another error at the backline.

After the change of sides, Sindhu managed to keep the two-point difference till 13-15 before a lucky net cord and a weak return at the net by Sindhu gave Tzu Ying a 17-13 lead.

Sindhu narrowed it to 16-18 and then 17-19 before Tzu Ying sealed the contest with the Indian going to the net twice.

Making his fourth appearance at the season finale, Srikanth jumped to 7-1 early on but a few unforced errors helped Antonsen to make it 4-7.

The Danish won a long 35-shot rally before Srikanth caught him off guard in the front court before gaining a three-point advantage at the break.

Antonsen drew parity at 12-12 with a smash but Srikanth played a magical return to move to 14-13 and then a backhand flick took him to 16-13.

A couple of smashes helped Srikanth to reach 19-13 and soon he grabbed five game point opportunities and sealed it with his rival going wide.

In the second game, Antonsen erased a 0-2 deficit to make it 5-2 with some superb shots from the front court. The Danish gained a four-point advantage at the interval following Srikanth wide return.

Srikanth showed good front court skills to narrow it down to 15-16 before missing the line with his smash. The Indian lost a point at the net and then went wide as Antonsen unleashed a jump smash to grab four game points and converted it with an acccurate shot at the backline.

In the third game, Srikanth enjoyed a two-point advantage at the interval but he made too many unforced errors to allow Antonsen level par at 13-13.

Two sensational rallies ensued with both the players winning one each before Antonsen reeled off four straight points to grab three match points. Srikanth saved one before hitting one long.