A brace from Neymar and a Luis Suarez goal had put Barca in control against Real Sociedad before Messi also got on the scoresheet in the 4-0 rout at Camp Nou on Saturday.
Messi's goal came via a tap-in after a Neymar cutback in the first minute of additional time, but Iniesta played down the importance of the Argentine always netting.
"I don’t think Leo has to score," Iniesta told the club's website.
"For us he’s the number one whether he scores or not."
A knee injury has led to a disrupted campaign for Messi, who has scored four league goals – far fewer than team-mates Neymar (14) and Suarez (12).
Saturday's win extended Barca's unbeaten run to 10 matches, including winning their past five by at least three goals.
Iniesta, whose side are four points clear at the top, said there was still work for Luis Enrique's men to do.
"We can continue to grow," he said.
"Even though there is a lot left in the season and we’re happy with the way things are going, but without getting ahead of ourselves."
