Malaysia's Liew Daren upset Antonsen, one of the pre-tournament favourites, by a score of 21-12, 21-18 to progress to the second round in Bangkok.

Another Malaysian also progressed in the men's singles - eighth seed Lee Zii Jia.

Lee came from a game down to defeat India's HS Prannoy 13-21, 21-14, 21-8.

Seventh seed Angus Ng Ka Long of Hong Kong won 21-15, 21-15 against The Netherlands' Mark Caljouw, while second seed Chou Tien-chen of Chinese Taipei staged a comeback against Thailand's Tanongsak Saensomboonsuk.

COVID-19 issues continued to punctuate the tournament as the BWF confirmed that one German coach and a member of the French entourage had tested positive for the virus, although no players did so today.

The delegation members who produced a positive polymerase chain reaction (PCR) test result are now required to stay in hospital for a minimum of 10 days.

The Badminton Association of Thailand has also defended its testing regime after Indian player Kidambi Srikanth yesterday complained of nosebleeds following a PCR test.

"The athlete had been swabbed three times earlier with the most recent one possibly causing irritation and fragility of the capillaries," read a statement from the national body.

"Therefore, when the swab was repeated on Tuesday, and factoring the athlete's tense nature, the position of the stick in the nasal passage was misaligned, which caused the slight bleeding noticed from the tip of the swab.

"The COVID-19 staff member did not notice any bleeding from the athlete's nose and there was no complaint from Kidambi at that point.

"After about three to five minutes, another athlete from the India team reported that Kidambi had a nosebleed.

"It is not known whether the athlete had blown his nose or stuck tissue up his nostrils, which could have caused more blood vessels to rupture."

Srikanth today beat compatriot Sourabh Verma in the men's singles.

In the women's singles, India's Saina Nehwal won her rescheduled first-round match against Malaysia's Kisona Selvaduray in straight games.

The London 2012 bronze medallist had initially been forced to withdraw due to a positive COVID-19 test, but was cleared upon further testing.

South Korea's An Se-young was a 21-15, 21-12 winner against Malaysia's Soniia Cheah, while Spain's Marín defeated France's Qi Xuefei 21-10, 21-12 so will join An in round two.

Fourth seed Ratchanok Intanon of Thailand was a 21-15, 21-15 victor in her tie against Yeo Jia Min of Singapore.

Mixed doubles eighth seeds Tang Chun Man and Tse Ying Suet of Hong Kong also made it through to the next round with a victory over B. Sumeeth Reddy and N. Sikki Reddy of India.

Second seeds Praveen Jordan and Melati Daeva Oktavianti of Indonesia are also through to round two after a victory over Niclas Nohr and Amalie Magelund of Denmark.

England's seventh seeds Marcus Ellis and Lauren Smith defeated Germany's Ralphy Jones Jansen and Kilasu Ostermeyer in straight games.

The men's doubles saw Chinese Taipei's sixth seeds Lee Yang and Wang Chi-lin defeat Denmark's Kim Astrup and Anders Skaarup Rasmussen, while South Korean seventh seeds Choi Sol-gyu and Seo Seung-jae eased past Canadian duo Jason Anthony Ho-Shue and Nyl Yakura.

In an all-Indonesian tie, second seeds Mohammad Ahsan and Hendra Setiawan defeated Pramudya Kusumawardana and Yeremia Rambitan.

Finally, in the women's singles, fifth seeds Greysia Polii and Apriyani Rahayu of Indonesia handsomely Canada's Rachel Honderich and Kristen Tsai 21-12, 21-11.

The tournament, the first of three BWF events being staged in Bangkok, continues tomorrow.