Two late extra-time goals by Peter Weatherson saw 10-man Morton come from behind to reach the second round of the Challenge Cup.
After a well-balanced 90 minutes the game was goalless and Stewart Greacen was sent off for a professional foul early in added on time.
David McNaught then curled in an impressive shot for the home side.
But Weatherson equalised with a rifled free-kick and then headed the Second Division side to victory.
Dumbarton: Shaw, Geggins, Brittain (Boyle 78), Canning, Craig, Bagan (McQuilken 95), Gentle (Quitongo 46), Winter, Dillon, McNaught, Borris. Subs Not Used: Dornan, Grindlay.
Booked: McNaught, Dillon. Goal: McNaught 114.
Morton: McGurn, Weatherson, Alex Walker, Alex Walker, Harding, Greacen, McLaughlin, Millar, Jamie Stevenson (Russell 118), McAlistair, Templeman (McClean 65), McGowen (Lilley 33). Subs Not Used: Keenan, Gonnet.
Sent Off: Greacen (105). Goals: Weatherson 117, 119.
Ref: E Norris