Ighalo who is still looking for his first Premier League goal, replaced Anthony Martial in the 78th minute of the game.
It was his seventh Premier League appearance for United since his loan move from Shanghai Shenhua.
Mason Greenwood’s sixth league goal of the season gave United the lead inside 16 minutes before Bruno Fernandes combined with Paul Pogba to double their tally before the half-hour mark.
Fernandes then extinguished Brighton’s second-half revival as his emphatic volley rounded off a devastating United counter within five minutes of the restart.
David de Gea prevented Aaron Connolly, Neal Maupay and the lively Leandro Trossard from registering a deserved Brighton consolation after an improved second-half display, but the damage was done as they tasted their first defeat since the restart.
The victory extends United’s unbeaten run to 15 games and lifts them up to fifth, two points behind fourth-placed Chelsea ahead of their trip to West Ham on Wednesday.
By James Agberebi
Copyright © 2020 Completesports.com All rights reserved. The information contained in Completesports.com may not be published, broadcast, rewritten, or redistributed without the prior written authority of Completesports.com.