The 'Red Devils' claimed a 2-1 win over the 'Seleçao' in Kazan, but it wasn't all plain sailing as the South Americans pegged their opponents back and threw everything at them in the second half.
However, Martinez's side stood up to the battle, leading him to hail the mentality of his players at full-time.
"They did incredible. There were amazing hearts out there. I didn't think for one minute their hearts would give way," said Martinez.
"You have to accept that Brazil have so much quality and finesse, they break you down, but we did not accept it. Not for one minute were [Belgium] going to give up.
"These boys deserve to be heroes in Belgium. The execution of the tactics was magnificent.
"It is special and we can't let the people of Belgium down. We can pass that down the generations - beating Brazil."
Midfielder Kevin De Bruyne, arguably Man of the Match on the night, concurred with his boss, saying: "I know it's not easy to play against Brazil.
"But we were magnificent in the first half and they changed tactics second half. We showed our character after they scored. We did very well with our running from deep, it is wonderful.
"We are here to try and win the World Cup and are very united."