Granada were not showing any early nerves and indeed had the first chance on 10 minutes, but Nolito's shot was saved by Victor Valdes after he had worked space at the far post.
Cesc Fabregas almost set up Lionel Messi for the equaliser, but the Argentinian could just not get a touch on the Spaniard's cushioned header.
Six minutes later the hosts took the lead and it was the lively Ighalo who finished off a swift break by turning in Carlos Aranda's pass.
Barcelona started to dominate and should have been level on 39 minutes but Tono came off his line well to deny Messi.
Despite their pressure the Catalans were unable to score before the break and went in a goal behind.