The frontman struck twice and could have added further to his tally as Boro turned on the style in the second half of the game.
Jake Day also took advantage of the sharp, yet intricate passing moves, to stroll through for his opening Boro goal.
Tasked with bouncing back from Saturday's disappointing defeat at Burscough, Boro set about their assignment in confident fashion.
Having avoided an early scare when Luke Molloy's hopeful cross skewed just over the bar, Boro moved ahead with 12 minutes on the clock.
Igiehon was on hand to finish off from close range after a delightful flowing move that cut right through the Spennymoor defence.
The big striker almost added his second within minutes, but his fierce drive scorched just past the upright of visiting keeper Daniel Lowson.
Boro again threatened when Cameron Murray was fed in the box, but his low shot was gobbled up by the Spennymoor custodian.
So it came as something of a shock when Spennymoor restored equilibrium just before the half-hour.
Steven Taylor squirmed into some space on the edge of the box, his drive took a wicked deflection to beat the outstretched palm of Jordan Porter.
Boro were unlucky not to reclaim the lead just before the interval when Adam Bolder rolled the ball towards the bottom corner from the edge of the box. Lowson leapt like a panther and somehow managed to turn it away with the tips of his fingers.
Igiehon came close when the action re-started, lashing just past the post and the pointed foot of charging midfielder Matty Bloor.
The openings began to pile up after this, beginning with Murray rounding the keeper, but bizarrely shooting well wide of the target.
Igiehon's deflected effort was cleared off the line by Alex Goundry, then the ball then flashed across the front of the striker when all that was required was a touch to steer it over the line.
Jameel Ible was played in by Chris Bolder, but his shot was saved by the feet of sub stopper Declan Greenwood.
But finally Igiehon managed to double his and Boro's total with 17 minutes left when he rose well and angled a header into the back of the net.
Spennymoor almost hit straight back, but Porter magnificently pushed away a superb drive from Taylor.
Striker Day was thrown into the fray for the final moments and he soon got in on the act when taking a throughball and lifting gently home to make it 3-1.
Igiehon crashed a shot just wide as the game moved into injury time, but by that point Boro's path through to the next round had already been plotted.