The South Korean women's singles shuttler overcame Sindhu in straight games to progress.
Sindhu couldn't rise up against the challenge presented by her opponent.
It was a bad day in office for the Indian contingent.
Here are all the details.
Sindhu beaten comprehensively by An Se Young
Sindhu was lagging behind 8-15 in the first game and could not come up with answers against the teenager.
She surrendered the first game 14-21.
Sindhu fought back in the second and kept the intensity going.
Things were level 8-8 at one stage and then SIndhu led 15-13.
However, An Se Young kept up with the intensity and played beautifully to win 21-17.
Sindhu's early exits a worry of late
Sindhu hasn't had an excellent run in 2019. Recently, she suffered early exits at the China Open and Korea Open last month. The Hyderabadi player, who is ranked sixth in the world, couldn't go far at the ongoing Denmark Open as well.
Poor day for India at Denmark Open
Earlier, Sameer Verma was trumped by Chen Long in straight games in a crunch men's singles second round encounter.
The Chinese star tamed Verma 21-12, 21-10 in straight games.
Besides Verma, Indian men's double pair of Chirag Shetty and Satwiksairaj Rankireddy bowed out.
The duo lost to Han Chengkai and Hao Dong Zhou 16-21, 15-21 in straight games.
Sai Praneeth blown away by Kento Momota
India's men's singles badminton player Sai Praneeth was blown away by Kento Momota of Japan in the second round. Momota was all over Praneeth and took a 9-0 lead in the first game, before winning 21-6. In the second game, Praneeth fared better but lost.
Saina and Srikanth were big casualties on Wednesday