Romelu Lukaku and Eden Hazard each netted a brace, with Lukaku moving into a tie on the top scorer leaderboard with Cristiano Ronaldo. England (three points) face Panama (none) on Sunday in the same group. They'll need another stout performance against a European giant to maintain hope of advancement going into the final match vs. Panama.
Tunisia did manage a late consolation when Khazri swept home Hamdi Nagguez's cross but, unless Panama beat England, they will become the third African team to be eliminated, leaving Nigeria and Senegal to carry their continent's hopes in this competition.
Belgium have six points from their two games while Tunisia have still to get off the mark and have only a remote mathematical chance of qualifying.
Belgium opened with a 3-0 win over Panama 3-0 and another win against Tunisia would nearly certainly secure a place in the knockout stages from Group G. VAR was used, confirming that the challenge was illegal and that it had taken place just inside the penalty area.
Any thoughts that the rampant Belgians would accelerate out of sight were dispelled - at least briefly - just two minutes later, though.
Belgium are now unbeaten over their last 21 matches.
Hazard left the game in the 68th minute, with Germany's Andre Schurrle and Toni Kroos, who did so in the 7-1 victory over Brazil in the semifinals in 2014, the last two players to score two goals each in a World Cup game.
With the game essentially wrapped up, Martinez opted to bring Lukaku off before the hour, the striker having picked up a knock on his foot earlier in the game.
A win would put the Red Devils in pole position to qualify for the last 16.