The Nigerian, who is on loan from Shanghai Greeland Shenhua, also provided the assist for the second goal, finished by Daniel James, and was unlucky not to add to his personal tally when showing great strength before rolling his effort against a post.
Ighalo's fourth goal since arriving on deadline day in January was a thing of absolute beauty.
He took three touches to juggle a pass by Bruno Fernandes on the edge of the area in order to work his way into a shooting position. With tremendous venom, the centre-forward hammered his drive in off the underside of the bar for a strike that deserved more attention than it received in a virtually empty stadium due to the tie being played behind closed doors.