The final scoreline will no doubt frustrate coach Tommy Wilson and his players as they dominated this match for long spells and created numerous chances throughout the 90 minutes.
But they could not find a way past Sons keeper Jamie Ewing and the visitors grew in confidence as the match progressed because of that.
It was lone striker Ryan Metcalfe that netted both goals on 63 and 84 minutes, the second coming from the penalty spot, and despite a late rally Rangers were unable to get back into the game as rain lashed down on the playing surface.
After three excellent victories against Annan Athletic, East Fife and Cowdenbeath the Gers second string started positively and they should have been in front at the half-time interval.
On 12 minutes the lively Tom Walsh cut inside from the left flank and his rising right foot shot from 20 yards flew over Ewing’s goal.
Wilson was then forced to make a change three minutes later when Gregor Fotheringham was taken off with an injury and he was replaced by Jamie Burrows.
The Light Blues continued to push forward and on 20 minutes an excellent cross from Chris Hegarty, who feature at fight back, found the in-form Calum Gallagher but his glancing header went wide of target.
After the half hour mark Rangers continued to ask questions of the Dumbarton defence and a terrific through ball from Charlie Telfer found Gallagher but Ewing did well to make a fine save as the striker attempted to take the ball past him in the 18 yard box.
With the break approaching Telfer then tried his luck with a long range effort which flew across goal before Kamil Wiktorski did the same, only his effort was spilled by Ewing and after a goalmouth stramash the ball was punted to safety.
In the second half Rangers changed their system with substitute Burrows being replaced by Jordan Wilson, again due to injury.
And with the game still goalless Dumbarton were still very much in this game and they knew it.
When Walsh blazed a shot over from 20 yards after a terrific bit of skill to get away from his marker you had a feeling this would not be Rangers’ day.
And after the hour mark the visitors took the lead.
A long ball found its way through to Metcalfe who made the most of slack defending before poking the ball confidently under Blair Currie.
Metcalfe then tried to double his side’s advantage with a powerful, dipping shot from distance which the Gers keeper did well to hold.
At the other end Darren Ramsay had his hands on his head when he powered a shot across Ewing but it bounced off the post and back into the keeper’s arms.
With the clock ticking down Dumbarton were given the chance to increase their lead with six minutes left when a cross came into the Gers box.
Sons number 10 Alistair McKerracher was sandwiched between two Rangers players at the back post and the referee immediately pointed to the spot for what appeared to be a push on the back from Hegarty.
The Northern Ireland under-21 captain couldn’t believe the soft decision and was booked as he protested.
Metcalfe, however, showed his composure to send Currie the wrong way from the spot.
RANGERS (4-3-3): Blair Currie; Chris Hegarty, Luca Gasparotto, Stuart Urquhart, Andrew Mitchell; Kamil Wiktorski, Gregor Fotheringham (Jamie Burrows 15 (Jordan Wilson 45)), Charlie Telfer (Craig Halkett 78); Darren Ramsay, Calum Gallagher, Tom Walsh
Subs Not Used: Liam Kelly, Kristian Gibson