Badminton world number one An Se-young had stern words for her watching father as her frustrations threatened to boil over in victory at the Asian Games in Japan on Wednesday.

The reigning world and Olympic champion defeated home player Akane Yamaguchi in three tough games in the semi-finals of the women’s team event in Nagoya.

But the 24-year-old was not always at her brilliant best against the world number three, winning 21-9, 18-21, 21-11.

“I think I expressed it too forcefully, to make myself notice that I was making mistakes,” she said of her visible frustrations.

“I should not have done that. From now on I need to hold it in more.”

An said the fact that she could hear everything in the crowd, including the commentators, was proof of her poor concentration.

Most of all, she said, she was aware of parents watching in the arena.

“Parents usually cannot bear to watch their own children compete, but my dad seems to watch perfectly happily, which is a bit much.

“I am out there running myself into the ground and he is just cheering away in comfort.”