Real Madrid forward Kaka was also on target, with his return to form at club level earning him a recall to the Selecao.
Brazil named a strong starting XI for a game staged in Sweden and were always in control of the tie.
Oscar, who has impressed since joining the Premier League ranks over the summer, all but ended the game as a contest with two goals in a productive first-half spell.
Kaka, whose last appearance for his country came at the 2010 World Cup, added a third early in the second half, with Iraq unable to gain any kind of foothold in the game.
A side managed by former Brazil skipper Zico were breached a further three times before the final whistle, with Hulk, Neymar and Lucas getting in on the act.
It could have been more were it not for an inspired performance from Iraq keeper Noor Sabri, with Brazil putting in the kind of performance expected from five-time world champions.
Mano Menezes' side will face Japan in another contest held on neutral soil on Tuesday, with that fixture taking place in Poland.