Spirited Duns put in a determined performance against the East League Division 1 champions at the Hardens.
Although the unbeaten visitors were on the front foot for most of the game, the home side defended well and refused to cave in under pressure.
Preston Lodge were made to work hard for their three tries in windy conditions to maintain their 100 per cent record, but for only the second time in the league this season they failed to secure a four-try bonus point.
No8 Jason Riley scored the only try of the first half before Paul Voy crashed over early in the second half to double the lead.
Duns refused to wilt, however, and it took a late score in the corner from winger David Lockie to seal the win.