The Argentine's performances in 2014 thus far had come in for criticism, so his Blaugrana team-mate was delighted by the 26-year-old's response at the Ramon Sanchez Pizjuan
The Argentine had gone through a barren run in La Liga, prompting dramatic claims that he had "lost his passion for football".
However, Iniesta says that the 26-year-old attacker will always respond to criticism and was delighted by the way in which the four-time Ballon d'Or winner inspired Barca to a come-from-behind victory that propelled the Catalans back to the top of the table.
"Messi always responds. He never misses and in just a few minutes he can change a game. He’s a fundamental player," the Spain international is quoted as saying by his club's official website.
"When you have a chance you have to take advantage of it. I think this victory will give us strength ahead of the match on Wednesday [against Real Sociedad in the Copa del Rey] and for the games to come after that.
"We will fight until the end. The important thing is to not lose a lot of points and to improve as a team."
Barcelona can book their place in the Copa del Rey final when they travel to San Sebastian to face Sociedad on Wednesday, having won 2-0 in the first leg at Camp Nou last week.