Romelu Lukaku and Eden Hazard both scored twice as Belgium sent out a message about their World Cup credentials with a 5-2 win over Tunisia on Saturday.
Hazard opened the scoring from the penalty spot (6) before Lukaku doubled their lead (16) with a tidy finish.
Dylan Bronn headed Tunisia back into the game (17) but Belgium always carried a huge threat in attack and Lukaku finished off a counter-attack to re-establish the two-goal cushion (45+3) with his fourth goal of the tournament.
Hazard added another (51) following a wonderful Kevin De Bruyne pass and Belgium could afford substitute Michy Batshuayi to miss a hatful of late chances before he finally score in injury time (90), as his side all-but guaranteed their spot in the last 16.
Whabi Khazri scored a consolation (90+3) for Tunisia, who, barring a minor miracle, are out of the World Cup following two straight defeats.
One potential sour note for Roberto Martinez was Lukaku hobbling off with an ankle problem early in the second-half. Belgium play England on Thursday in their final Group G encounter.
Belgium flew out of the traps in Moscow as Hazard won a free-kick with just 15 seconds gone, and won another foul in the penalty area on six minutes when he was tripped on the line of the penalty box.
The decision survived a VAR review and Hazard stroked home the spot kick.
Dries Mertens then released Lukaku in behind on 16 minutes.
The Manchester United striker drove down the left and reversed a clever shot into the far corner.
Tunisia would have been fearing a thrashing at that point but got themselves back in the game 60 seconds later when Bronn took advantage of a poor offside line by Belgium to head home from a Khazri set-piece.
With Tunisia pressing on, Belgium were a constant threat on the break and Lukaku and De Bruyne wasted a couple of good openings.
Lukaku kept on making runs in behind and was found just before the break by Thomas Meunier.
This time, Lukaku found the killer finish to lift the ball over the goalkeeper to restore Belgium's two-goal cushion.
De Bruyne came to the party in the second half with a spectacular raking pass that released Hazard through on goal.
From there, the Chelsea man rounded the goalkeeper to make it 4-1.
That goal knocked the stuffing out of Tunisia, who threw the towel in during the final quarter.
Lukaku - who limped off - and Hazard were both withdrawn by Martinez to save their legs but the chances still came for the Europeans.
Batshuayi smacked the crossbar from five yards out and missed a further four guilt-edge opportunities before finally tucking one away in stoppage time.
Khazri scored with the last kick of the game but this was all about Belgium, who laid down the first real marker of the tournament with this convincing victory.
Both teams play their final games on Thursday evening. Belgium play England while Tunisia take on Panama.