South Korea's Son, a bronze medallist at last month's World Championships, took the first set but struggled thereafter against Indonesian opponent Anthony Sinisuka Ginting.

The world number 24 eventually triumphed 16-21, 21-18, 21-13 in 1hour 18min at the SK Handball Stadium.

Another Indonesia unseeded player joined Ginting in the semi-final after also surprising a higher ranked opponent.

World number 22 Jonatan Christie required just 32 minutes to defeat Taiwan's seventh seed Wang Tzu Wei 21-13, 21-17.

It followed his victory at the recent Southeast Asian Games in Kuala Lumpur.

There were more shocks at the last-four stage in the corresponding women's singles draw.

Second seed Akane Yamaguchi lost in two tight sets to fellow Japanese player Nozomi Okohara.

The eighth seeded Okohara won 21-17, 21-18 to set-up a final with India's fifth seed Pusarla V. Sindhu.

She won 21-10, 17-21, 21-16 in 66 minutes against sixth seed He Bingjiao of China.

Both finals will take place tomorrow.