Forfar maintained their perfect record to keep the pressure on Stirling Albion at the top of the Second Division table.
Paul Tosh grabbed his seventh goal of the season to hand Forfar victory, but it was goalkeeper Michael Brown who was the real hero with some superb stops to keep Dumbarton out.
Tosh struck after 54 minutes when he was sent clean through on Stephen Grindlay by Paul Shields after Iain Russell had lost possession for Dumbarton.
But Brown had to be at his best to deny chances from substitute Andy Rodgers and Barry Donald while Rodgers also crashed a 20-yarder off the crossbar.