Farrell has been chosen as the man to lead the Red Rose for the three-Test tour this month in place of regular skipper Dylan Hartley, who has been ruled out due to a concussion.
England go into the first clash with the Springboks on Saturday on the back of a 63-45 defeat to the Barbarians, extending their losing record to four straight matches.
Despite the poor form, Itoje has backed Farrell to lead the country to a series victory in South Africa and restore the confidence in the squad.
"I think Owen plays better when he's captain. He normally speaks well, but I think he speaks better as captain," he was quoted as saying by www.rugbypass.com. "He has a holistic approach to the game.
"I haven't met many, if any, smarter rugby players than him. I know for a fact, having played under him before, that he is going to do very well in the role."