Jordan Pickford was named England goalkeeper for the match and looks to be Southgate's first choice going into the World Cup, ahead of Jack Butland and Nick Pope.
Following an inconsistent season with Tottenham and some diffident displays for England, Alli needed to cement his place in Southgate's team and, ignoring the hail of boos, he was making a convincing case.
Captain Mikel prepares for his second World Cup and will anchor the midfield with support from Ogenyi Onazi, recuperating Wilfred Ndidi, John Ogu, Oghenekaro Etebo and Joel Obi.
Trippier claimed the assist for England's opening goal when his corner was headed home by Gary Cahill, and Southgate said: "His quality on the ball is outstanding".
The visitors came flying out of the bocks after half time and halved the deficit within two minutes of the restart when Ighalo's effort came back off the post and bounced to the feet of Arsenal's Iwobi, who swept the rebound home.
Sterling was headline news for the wrong reasons as England's preparations for the World Cup were dealt a double blow. He has kept working hard, kept his focus and I think you saw a performance that, apart from scoring a goal, he was very lively.
"I don't think we got a lot of answers today though because Nigeria just lied down in the first period and let England do what they want".
"In the second half we played five at the back as well that's what we did and we played much better, we created chances and we scored a goal".