Belgium sent a World Cup warning to England by putting five past Tunisia in Group G.
Romelu Lukaku and Eden Hazard both scored twice for Roberto Martinez's men before substitute Michy Batshuayi wrapped it up late on.
Hazard opened the scoring from the spot early on for Belgium after he had been taken out on the edge of the box.
Lukaku then made it two, finishing well after good work from Dries Mertens.
But Tunisia hit back within an instant as they capitalised on some shaky defending from Belgium.
Wahbi Khazri's ball into the box was poorly defended and Dylan Bronn glanced a header past Thibaut Courtois.