He was also an international team-mate of the six-time Ballon d'Or winner until he stepped away from representing his country in 2018.
Now at Estudiantes de La Plata, Mascherano remains in awe of Messi, saying the Barca star can dictate matches to his own tempo in a way few others can hope to do.
He told radio programme Cielosports: "The majority of good players make good decisions, but they don't execute them in the best way, or vice versa – the execution is good, but it doesn't end up being the best decision.
"What makes the difference in football is decision-making and execution, and Leo does both things well, and at an incredible speed, and that's why he's different.
"Normally, the game dominates us and takes you with it, but in Leo's case it's the other way around: he decides what to do or what not to do with the game.
"He knows how to save his strength and that allows him, during a match, to have seven, eight or 10 important actions at 100 per cent. That's how he can dominate the game."