The first of the Indians to qualify for the semis was top seed Mangaonkar, who beat Finland's Matias Tuomi 11-6 11-7 11-2. Sandhu joined his Indian teammate in the last four with a 11-5 11-5 11-8 win over Carlos Cornes Ribados of Spain.
Mangaonkar started off perfectly against Tuomi to go 6-0 in the first game. Tuomi played better in the second game, trading points with Mangaonkar with some delightful rallies.
He next meets England's Angus Williams who beat crowd favourite Velavan Senthillumar 11-5 11-8 5-11 11-3.
Sandhu faces the the winner of the match Kristian Frost Olesen of Denmark and Adam Murrills of England.
In the women's draw, France's Chloe Mesic beat Pakistan's Sadia Gul 11-7 11-7 11-7 and will next meet top seed Birgit Coufal of Austria. Coufal defeated Indian Sachika Ingale 11-2 11-4 11-2 in 20 minutes.