Watch: Sensational Mertens Volley
The debutants Panama managed to frustrate Belgium, ranked third in the world, in the first half and the score was 0-0 at the break.
But when the deadlock was broken in the 47th minute it was done so in some style.
A cleared cross looped toward Mertens on the right-hand edge of the area just inside the box, who without hesitation hit a sumptuous volley which dipped over Penedo and into the far corner of the net.
Panama had a couple of half-chances to pull even, and they appeared to be holding Belgium at bay–that is, until the favorites doubled their lead in the 69th minute. De Bruyne hit a majestic assist off the outside of this foot, finding a diving Romelu Lukaku who steered in the header to make it 2-0.