The Everton forward struck twice as Marc Wilmots' men booked their place at World Cup 2014 but was modest in victory
The forward, on loan at Everton from Chelsea for the season, struck twice in the first half as Marc Wilmots' team secured top spot in Group A and a place in Brazil next summer.
Niko Kranjcar volleyed in a late consolation for Croatia in Zagreb but it was Lukaku's double that made the difference, although the striker opted to pay tribute to his team-mates rather than taking the credit for the three points himself.
"I'm not the match-winner, the team makes a difference. We played well," he told Belgian newspaper Het Nieuwsblad. "The players and I can finally stamp our personality on the team, I am proud.
"The last quarter we were difficult [to break down] but two years ago we could still have lost here 2-1. Now we have shown that we have a winning mentality.
"On Tuesday we play at home in the last match [against Wales] but it is certainly not a meaningless match. We will do everything to win."
Belgium coach Wilmots echoed Lukaku's sentiments and insisted that celebrations would be put on hold until after their clash with Wales on Tuesday.
"We are happy but we will not be partying," the coach said. "We have had a moment in the locker room, but it is still too early for euphoria.
"On Tuesday we have another game and I hope we also tackle it seriously. They played very maturely."