Monaghan, who competes in the over-50 category, finished in a time of 16.55, which was 26 seconds in front of Ben Morrish in second.
Former Commonwealth Games marathon runner Stuart Hall, another over-50 veteran, was third in 17.29.
Erme Valley Harriers’ Owen Parkin came home in fourth (17.34), just ahead of Plymouth Musketeers’ Alan Ryder in fifth (17.36).
First women home was Tavistock’s Alice Rogers, who clocked 19.28. There was a sprint finish for the second female spot, with Plymouth Harriers’ Jane Allison (20.26) just edging out Tavistock’s Natasha Farrington by a second.
There will be five more 5k races in the series at Saltram. The next one will take place on May 13.
TO VIEW FULL RESULTS CLICK HERE http://www.armadaathletics.co.uk/wp-content/uploads/2015/04/5K-Summer-Series-Apr-15.pdf
TO VIEW MORE ATHLETICS STORIES CLICK HERE http://plymouthsportsgazette.com/category/athletics/