The pair both came off the bench to score in the last 16 as the Red Devils came from 2-0 down against Japan to win 3-2.
And they have been rewarded for their contributions by stepping into Roberto Martinez's side in Kazan.
West Brom winger Chadli comes in as a straight swap for Yannick Carrasco on the left-hand side having scored the dramatic late winner on Monday.
That means a more advanced role for Kevin De Bruyne, who alongside Eden Hazard will provide support for lone striker Romelu Lukaku.
Brazil, meanwhile, make two changes from their win over Mexico in the last 16.
Marcelo is fit to return to the starting XI having missed the 2-0 win in Samara, and comes straight back in for Filipe Luis.
Selecao boss Tite has resisted the temptation, though, to replace Gabriel Jesus with Roberto Firmino despite the former having failed to find the net thus far in Russia.
Brazil XI: Alisson; Fagner, Thiago Silva, Miranda, Marcelo; Paulinho, Fernandinho, Coutinho; Willian, Jesus, Neymar.
Belgium XI: Courtois; Alderweireld, Kompany, Vertonghen; Meunier, Fellaini, Witsel, Chadli; De Bruyne, Hazard; R Lukaku.