Yannick Bolasie had the first real chance for Plymouth in a poor opening 45 minutes, but was denied brilliantly by Tony Roberts' low save.
On the stroke of half-time John Akinde caught Curtis Nelson in possession, raced forward and exchanged passes with Jon Nurse before firing a low effort which David Button smothered.
Three minutes into the second half Plymouth got their vital goal. Nurse was penalised for a foul on Kari Arnason 25 yards from goal and the resulting free-kick was powered home low by Patterson.
The Daggers were denied an equaliser thanks to a fine double save from Button 10 minutes later, firstly denying Akinde and then rising quickly to his feet to save Danny Green's follow-up.
As the home side piled on the pressure Darren Currie, Peter Gain and Romain Vincelot all had efforts blocked and despite going down to 10 men after Patterson was sent off late on for fouling Green, Plymouth held on.
Dag & Red 0-1 Plymouth: Match Report - view commentary, squad, and statictics of the game as it happened.