Messi converted a first-half penalty before Julian Alvarez (22) scored either side of the interval to see off an overwhelmed Croatia, who had little left in the tank after progressing through the two previous rounds on penalties.
"We're an intelligent squad, we know how to read the game we know how to suffer when necessary, when to press. Every detail counts in every match," Messi, on a mission to win his first World Cup, told a news conference.
"We knew that sometimes they were not really tidy and would leave space behind."
Messi made the most of that space to set up Alvarez for the third goal after a superb run to the byline that capped a remarkable performance.
"I am enjoying this a lot. I am feeling really good, strong enough to face every match," Messi, who drew level with France's Kylian Mbappe (23) as the tournament's top scorer with five goals, said.
"In the previous match (against the Netherlands), extra time wasn't easy. Today we were tired, but we pulled ourselves up to earn this victory.
"We played very well, we prepared to play this way because we knew we wouldn't have the ball and would need to run in this match.
"So we prepared for this match in a very good way. As we always do," added Messi, who drew level with Germany's Lothar Matthaus as the joint record holder for most World Cup appearances with his 25th game.
Argentina are looking for their third World Cup title, and first since 1986, with a rejuvenated Messi spearheading their pursuit.
"Personally I'm very happy, I'm enjoying it a lot and I'm happy that I'm able to help my squad make things happen," said Messi, whose side started their campaign with a shock 2-1 defeat to Saudi Arabia.
"The first match was a hard blow. For us to start this way was hard, we didn't think we would lose against Saudi Arabia, it was a test but we proved how strong we are," Messi, his country's record World Cup scorer with 11 goals, said.
"It was very difficult because every match was a final for us. We were aware that if we didn't win it would be more complicated."
Argentina will face either France or Morocco on Sunday.
