Paul Ince kicked off his Blackburn Rovers career with a friendly victory over former club Macclesfield.
England winger David Bentley was not involved because of a calf problem.
Roque Santa Cruz was also absent, still recovering from his World Cup exertions with Paraguay.
Christopher Samba saw a low header sail just wide and Benni McCarthy hit a post before Dunn worked his way through to fire in a clever goal three minutes from the break.
Rovers sent out a totally different 11 in the second period and were two ahead inside a minute when Gallagher header home a Tony Kane cross.
League Two side Macclesfield, who eventually avoided the drop last season under new boss Keith Alexander, pulled one back soon after when Martin Gritton side-footed home a Francis Green cross.
The appearance of Wayne Rooney's brother, John - who has just been given a two-year contract at Macclesfield - almost produced an equaliser with a late shot on the turn.