The Olympic silver medallist was knocked out in the first round by Beiwan Zhang of the USA on Wednesday.
Heading into the tournament seeded fifth, the 24-year-old Indian went from having a first-game advantage to losing 21-7, 22-24, 15-21 to world number 10 Zhang.
Sindhu became the first Indian to win gold at the Badminton World Championships in August, but has suffered a dip in form since then.
To compound matters further as she gears up for Tokyo 2020, her coach Kim Ji Hyun has announced her resignation due to personal reasons.
The bad news for India didn't stop with Sindhu’s loss, as the men's singles event produced further disappointment. B Sai Praneeth, also coming off an early exit at the China Open, was forced out as well.
The 27-year-old had already lost the first game 9-21 against Denmark's Anders Antonsen and whilst trailing 7-11 in the second, he opted to pull out due to an injury.
Like Sindhu, Praneeth too is on a run of poor results following a high point, after defeating Anthony Sinisuka Ginting and eventually clinching bronze at the BWF World Championships in Basel last month — India's first medal at the event in 36 years.
Nehwal forced out
Olympic bronze medallist Saina Nehwal had to retire during her match with the scoreline reading 21-19, 18-21, 1-8 to grant South Korea’s Kim Ga-Eun a place in the pre-quarterfinals.
Nehwal, who lost to Thailand’s Busanan Ongbamrungphan in the opening round of China Open, won the first game 21-19 in a neck-to-neck battle, but went down fighting in the second despite leading the game by the break.
After stretching her lead to 13-8, the former World No. 1 gave away four consecutive points to bring the game to 13-12. Three more points and the South Korean raced into the lead before clinching the game in style.
The eighth-seeded Indian trailed 1-8 in the final game before deciding not to continue further.
Nehwal has had a tough time with illness and injury this season, being laid low with issues affecting her hip, shin, ankle and wrist.
In the men’s singles draw, Nehwal’s personal coach and husband, Parupalli Kashyap, held his head high to cruise into the second round of the competition.
The 2014 Commonwealth Games gold medallist defeated Chinese Taipei’s Lu Chia-hung in straight games (21-16, 21-16) and is now India’s lone survivor in the singles category. In what was an utterly nerve-wracking contest, Kashyap blossomed late in the match to clinch the first game before marching through a relatively easy route in the second.
Kashyap will now face Malaysia’s Liew Daren in the pre-quarterfinals on September 26.
Meanwhile, the men’s doubles pair of Manu Attri and B. Sumeeth Reddy too failed to advance after losing their opening round tie 16-21, 21-19, 18-21 against China’s Huang Kaixiang and Liu Cheng. India’s woes further carried on as Satwiksairaj Rankireddy and Chirag Shetty once again lost their men’s doubles tie (19-21, 21-18, 18-21) against Takeshi Kamura and Keigo Sonoda of Japan.