The Red Devils overturned a two-goal deficit to book their place in the quarter-finals in Russia, and the former Everton boss attributed the result to his side's attitude and desire.
"The reality is we went 2-0 down and you have to find solutions, you have to find a reaction, but what you need more than anything is the desire and togetherness of a group of players who are desperate to perform," he told reporters.
"If you look at the stats there are not many games where you can come back from 2-0 down at a World Cup. I think this is down to the personality, to the focus, to the desire, to the never-give-up attitude of the players and almost the belief of the players when the came on.
"Doing it within the 90 minutes was an incredible achievement."
Belgium will face Brazil in the quarter-finals.