Atfer the home side hit the post early on, Haggerty opened the scoring from Andy Nicholas' left wing cross before trialist Watts made it 2-0 from Andy Liddell's ball in.
Warne added a third from close range after good work by Mitchell Austin before the Millers made two half time changes, including Oliver Banks, son of Emley manager and former Miller Ian.
Liddell's late spot kick completed the scoring with four minutes left after a foul on Dale Tonge.
Team: Annerson, Tonge, Joseph, Haggerty (c), Nicholas, Liddell, Parr-Gallagher (Banks 45), Harrison, Austin (Gladwin 45), Watts (Brooks 61), Warne (Hiley 69).
