United had never lost a two-legged European tie after winning the first leg away from home, and knew they would reach the final by keeping a clean sheet at an expectant Old Trafford.
The hosts looked nervy as Celta made an attacking start, before Fellaini settled the tension by converting his side’s first effort on target.
The Belgium midfielder sneaked in at the far post to powerfully head in Rashford’s clipped left-wing cross.
Jose Mourinho’s side created few other chances as they aimed to frustrate the visitors with an organised and largely defensive approach.
Although Henrikh Mkhitaryan, Rashford and Fellaini all drew saves from Celta keeper Sergio Alvarez after the break, it was a functional – not flashy – performance.
For a better society