Tynesiders' first clean sheet of the season at this level. However, Peter Beardsley's side also went close when Aarons tried his luck from long range and clipped the woodwork.
Pereira was withdrawn for Jack Rudge towards the end, with the substitute firing over the bar in stoppage time after a Varela cross was only partially cleared, as a lack of a cutting edge again proved costly for the visitors as Newcastle saw out injury time to clinch victory and leave United in seventh spot in the table.
United: Amos; Varela, McNair, Ekangamene, Rowley; Janko, James, Pearson, Rothwell, Weir (Harrop 54); A.Pereira (Rudge 80). Subs not used: Gollini, Goss.