Asked if it was Argentina's most accomplished display of the tournament, the Barcelona forward told reporters: "I think it was.
"We produced a very complete match. We weren't able to create that many chances, but they didn't make that many clear chances either."
Argentina have now won all five of their matches at the tournament, but they laboured in the group phase and were criticised for a lacklustre display in their 1-0 victory over Switzerland in the last 16.
Beaten coach Marc Wilmots dismissively branded Argentina "an ordinary team with one extraordinary player" after the game, but Messi appeared similarly unimpressed with Belgium.
"All they had were long-range shots," he said, after a match settled by Gonzalo Higuain's eighth-minute goal.
"They have a lot of tall players, but couldn't do anything with them. We didn't give them space. The most important thing here is that we won and we got through."
It is 24 years since Argentina last reached the semi-finals of a World Cup and Messi said that he and his team-mates took great pride in matching the achievement of Diego Maradona's 1990 side.
"This is amazing," he said. "We knew it was going to be difficult.
"Argentina have gone a long time without doing this, and it was us who crossed the frontier."