Eden Hazard feared Belgium could suffer a repeat of their shock loss to Wales at Euro 2016 when they trailed 2-0 to Japan at the World Cup.
Goals from Genki Haraguchi and Takashi Inui in a seven-minute spell after half-time put Japan on track for their first ever World Cup quarter-final.
But after a double change from Roberto Martinez, Jan Vertonghen headed Belgium a lifeline, with substitutes Marouane Fellaini and Nacer Chadli then completing the comeback.
Hazard set up Fellaini for the equaliser but he conceded Belgium were worried they were heading out of the tournament in similar circumstances to their shock quarter-final loss to Wales at Euro 2016.
“To be fair we were thinking two years ago against Wales,” Hazard told a news conference. “But we were also thinking that we could score goals to win.
“We have players who can change the game, players on the pitch and from the bench can make the difference. Today we’re just happy to have won the game and to go on to the quarter-final.
“During the first 20 to 25 minutes of the first half, we were quite good. But what went wrong was at the beginning of the second half – this is where we conceded two goals. And those two goals were avoidable.
“We had some little defensive errors but the reaction we showed tonight was great. Maybe we needed this type of match for the future. We could have been eliminated, but we ended up in the quarter-finals. So we’re all very happy.”
Brazil await in Kazan on Friday, with Hazard set to come against Chelsea team-mate Willian.
“Now when it comes to the [next] match it is going to be magnificent,” Hazard added.
“Playing against Brazil is always amazing for players. We are going to rest really well and try to win that match.