The News Agency of Nigeria (NAN) reports that it was the 11th time this season Iheanacho was benched in the EPL.
Jonjo Shelvey scored an eighth minute goal to give the Magpies the lead, while Ayoze Perez sealed the win in the 75th minute of the encounter.
Jamie Vardy however scored a consolatory goal for the hosts in the 89th minute of the encounter played at the King Power Stadium.
Iheanacho has so far made only 15 EPL appearances this season, scoring just one goal, while Super Eagles midfielder Wilfred Ndidi was suspended for the clash.
At the Vitality Stadium, AFC Bournemouth forced Crystal Palace to a 2-2 draw.
Luka Milivojevic scored for Crystal Palace two minutes after the restart but Lys Mousset pegged the Eagles back in the 65th minute before Wilfred Zaha made it 2-1.
Joshua King however rescued a point for hosts Bournemouth in the 88th minute.
Also, Huddersfield Town held Brighton Hove Albion to a 1-1 draw at the Amex Stadium.
Jonas Loessl scored an own goal to give Huddersfield Town the lead in the 29th minute before Steve Mounir drew his side level three minutes later.
At the Bet365 Stadium, Tottenham Hotspur beat Stoke City 2-1 to consolidate their place in the race for a top-four finish.
After a goalless first half, Christian Eriksen scored the opener in the 52nd minute.
But Mame Biram Diouf restored parity five minutes later, before Eriksen made it 2-1 in the 63rd minute.
The result meant Tottenham maintained their fourth place position and are now tied on 67 points with Liverpool who drew goalless with Everton in the Merseyside derby earlier on Saturday.
At Vicarage Road, Watford lost 1-2 at home to Burnley as goals from Sam Vokes and Jack Cork for Burnley cancelled out Roberto Pereyra’s 61st minute goal.
At the Hawthorns, West Brom played out a 1-1 draw with Swansea as Nigerian-born English striker Tammy Abraham salvaged a point in the 75th minute for the Swans.
Abraham’s leveler came after Jay Rodriguez’s opener in the 54th minute.(NAN)