The game's scoring was opened by an Antoine Griezmann penalty, following Kylian Mbappe being brought down in the box, before Angel Di Maria's superb strike put Argentina on level terms.
Following a free-kick given away by Benjamin Pavard on the right flank, the ball came out to Lionel Messi on the edge of the box.
His shot was a tame one, that looked like it would pose Hugo Lloris no problems in the French goal.
However, Mercado managed to stick out a boot to direct the ball home and leave the French captain helpless in the goal, with the defender running off to celebrate with his team-mates.