Belgium are ranked third in the world, behind only Germany and Brazil, but Martinez said there was no room for complacency against Tunisian, ranked 21.
But their convincing start in Russia - Roberto Martinez's side have scored eight goals in two games - will hold critics at bay for the moment, with their biggest test coming in the final group game against England this Thursday.
Belgium against Tunisia was full of stats.
Belgium's last World Cup game against Tunisia was in 2002 when they played to a 1-1 draw.
Chelsea forward Hazard, who was named the man of the match, said: "I think the match was easy because we scored after five minutes and we knew Tunisia needed to win and would leave spaces and would be open".
The victory means Belgium stay top of Group G with six points taken from two games - and it is England who await them in their final group outing next week.
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After also scoring twice in the opening 3-0 win against Panama, Manchester United's Lukaku showed clinical finishing with two first-half goals in Moscow, matching Ronaldo's tally in Russian Federation. Tunisia cut the deficit when Dylan Bronn headed in from a free-kick.
Tunisia, also without a point after two matches, having extended their 40-year World Cup winless run to 13 games, are also still in with a theoretical chance of making it on through three points.
Lukaku was forced off in the 59th minute due to an ankle ligament injury but Hazard praised the improvement shown by his teammate.
Lukaku's absence would be a blow to Belgium's hopes against England, with top spot in the group likely to be up for grabs.
In the only other change, Naim Sliti has been replaced on the left wing by Saif-Eddine Khaoui.