Ranked no. 2 in the world by FIFA and backed by many to go on and win the tournament, Marc Wilmots' side flattered to deceive in its opener against Italy, putting in a limp display on its way to a 2-0 defeat.
Ireland, conversely, went into the game in relatively high spirits. A positive display against Sweden was only lacking the luck of the Irish, as Ciaran Clark's unfortunate own goal denied them all three points.
In the opening 45 minutes, it looked as though Belgium would once against disappoint, with pressure growing on Wilmots should he arguably continue to not make the most of this "golden generation" of players.
However, two minutes into the second half the team's quality eventually told.
It was a controversial opener, with Ireland feeling aggrieved not to have been given a penalty for a high foot on Shane Long.
In the blink of an eye, while several Irish players were still remonstrating with referee Cüneyt Çakir, Belgium counter-attacked through Kevin De Bruyne.
The Manchester City star's piercing run bypassed the entire opposition midfield, before setting up Lukaku who curled the ball brilliantly past Darren Randolph's despairing dive.
While Ireland still posed a threat, the Belgians began to exert their dominance on proceedings and doubled their lead just after the hour mark.
Patient play around the edge of the Ireland box culminated in Thomas Meunier crossing into the box, with Witsel running onto the ball and powering a header into the bottom corner.
Not long after it was game over, Eden Hazard this time leading another blistering counter-attack, bypassing Clarke's lunge on the halfway line and eventually squaring for Lukaku to tap home for his second goal.
Saying that the Belgium squad was full of "big personalities," Lukaku told ITV that the team was now on the "same page" after Saturday's win.
Given Belgium's ranking -- only Argentina is above them -- and the ludicrously talented group of players at his disposal, Wilmots will look to maintain the momentum gained from this win in the final group game against Sweden.
Belgium's victory in Bordeaux ensures Italy goes through as Group E winner, with the Republic of Ireland needing a win against Antonio Conte's side to have any chance of reaching the last 16.