Their second game in as three days - following Thursday's win over Dunipace - took its toll as the pre-season signs of bad passing and poor first touches again shone through in a torrid display.
Despite a promising start in the opening minute, Rob Roy failed to make an impact on the game that was soon dominated by the home side.
It was no surprise when Rangers took the lead in the 9th minute with a superb curling shot from the edge of the box from Alan McFadden.
Frustration was growing within the Rabs ranks and it was not great to see disputes between team-mates being openly displayed.
This perhaps contributed to the home side doubling their lead in the 20th minute when Phil Dolan slotted home from a cut back with the Roy defence posted missing.
Worse was to follow in the 38th minute when Ross Gallacher failed to clear and Kilsyth took advantage with Iain Diack thumping the ball home.
Scott Walker had to go off with a head cut and was replaced by Sean McCall and it took until the 44th minute for the Roy to put any pressure on the home keeper when Weir did well to save low down from Kevin Watt after good set up play from Joe Slattery.
In the second half Willie Sawyers replaced Watt as Rob Roy looked to reduce the deficit and soon Gary Carroll tested Weir in the Kilsyth goal. However Kilsyth were still dangerous on the break and Diack shot wide when sent clear on goal.
In the 66th minute Danny Boyle was unlucky to see his header miss the target but the Rangers responded quickly with Smith hitting the post and Rabs keeper Michael McKinven doing well to gather the rebound.
The visitors were pressing to make an impression on the game and further Rob Roy attacks ended up with efforts from Lee Gallacher and Shaun Fraser being wide of the mark.
After a superb run and cut back from Sawyers in the 84th minute there was no one in the box to take advantage and two minutes later Slattery was sent clear on goal but Weir saved well.
With three minutes to go Rob Roy were awarded a penalty when substitute Andrew Johnstone was brought down in the box after a neat drag back.
However the Rabs misery continued when Weir dived to his right and saved Sawyers’ spot kick.
Overall a very disappointing display from a Rob Roy side that showed the impact of injuries and holidays within the squad and others not taking their chance to impress.