Crewe Alexandra claimed only their second away league win since October as a 77th-minute volley from O'Reilly downed Crawley Town at the Broadfield Stadium.
The narrow victory keeps Crewe firmly in the pack chasing the top seven, while Crawley suffered their first defeat in four games after struggling to create clear-cut chances.
Crewe Set the Early Tempo
Crawley keeper Jacob Chapman was the busier of the two goalkeepers in the opening exchanges, making straightforward early saves from Owen Lunt and O'Reilly.