Tomorrow in Brasilia, they are up against a young, sparkling team who are considered a dark horse for the title. Even though they needed extra time to prevail against the United States, Belgium unleashed offensive qualities that could present major problems for Argentina's, at times, shaky defence.
Belgium fired 38 shots, half of them from midfielders Kevin de Bruyne and Eden Hazard, and strikers Divock Origi and Romelu Lukaku. An impressive performance by US goalkeeper Tim Howard kept the score down. Meanwhile, Argentina's attack hasn't been as fearsome as predicted. Centre forward Gonzalo Higuain is scoreless after four games and his attacking partner Sergio Aguero is injured. Ezequiel Lavezzi replaced the Manchester City striker but was ineffective against Switzerland.
Then there's Messi.
The little genius has delivered, scoring in every group stage match and setting up Angel Di Maria's extra-time winner against Switzerland in the round of 16.
In a tight game, the Swiss shackled him successfully until his decisive run in the 118th minute.
"We knew that we would face a situation like that, but that's football and we had luck on our side," Messi said. "We're aware that all matches are going to be close and that details will make the difference."
Wilmots was unwilling to compare the strengths of the two teams but noted that except for a few players, Argentina's performance at the World Cup has exposed some weaknesses.
"Obviously they have Di Maria, Lavezzi, Higuain and Messi," Wilmots said. "But I also saw they showed a lack of balance within the team and that they had problems."
If Messi is in extraordinary form, he will cause problems for Belgium, Wilmots conceded. "But if you ask me as a coach whether I prefer a good collective or one great player, I prefer the team."
Argentina left back Sergio Rojo is suspended and will probably be replaced by Jose Basanta in tomorrow's game.
Wilmots said Belgium left back Thomas Vermaelen is likely to return after missing the US game with a hamstring injury, while midfielder Steven Defour is back from suspension.
Tomorrow
-In Brasilia: Argentina v Belgium, 4am.