Manager Lee Driver-Dickerson stuck with the same team that started the Winchester game in mid-week with the addition of Johan Flo to the squad after returning from Norway during the week.
Despite a number of spells of good passing play around the pitch, the final ball forward was lacking and the creative touch was missing leading to a number of unforced errors.
An early Marlow corner saw Toby Lawrence head clear with the follow up shot from full back Curtis Chapple sailing over the bar. Marley Thomas put his shot over the bar at the other end from a well worked Ben Hands free kick.
In a spell of pressure from the visitors mid way through the first half Edji Mbunga had a shot blocked by the home defence Ben Deakin followed up and shot wide. Ben Prictors cross from the left found Mike Ford but headed over the bar in space.
Marlow produced the first shot on target on 25 minutes, Kameron English firing straight at Lewis Adams. The Swans were forced into an early change on 29 minutes, Deakin suffering a leg injury and was replaced by young Issac Thurston for his first team debut.
Marlow started to get a grip on the game on the half hour mark and duly took the lead on 33 minutes. An unforced mistake from Lawrence saw Nnamdi Nwachuku collect the ball on the edge of the box and slot the ball past Adams.
As the half drew to a close Marlow doubled their lead a floated free kick on the left towards the far post was headed down across the goal where Junaid Bell was lurking to tap the ball into the net.
The second half continued where the first half ended with Adams being called into action a number of times. Both Bell and Nwachuku fired long range shots that Adams calmly smothered.
Thurston pushing forward headed narrowly wide from Ben Prictors long cross field ball. On 54 minutes Adams tipped Jordan Browns shot around the post after another defence mistake by the Swans giving the ball away in a dangerous position.
A minute later Johan Flo and Jamie Martin were brought on to give the visitors some much needed creativity and pace up front.
Nathan Dennis committed a foul on the edge of the box fortunately the free kick was hit high over the bar and into the car park. However it was on 70 minutes that Marlow wrapped the game up with a third goal. Isaac Olorunfemi collected a long range ball forward on the left and then squeezing a shot inside the near post past Adams.
Marlow continued to cause the Slimbridge defence trouble Chapple fizzing a ball across the 6 yard box then English forcing a stop by Adams with only 10 minutes remaining.
A free kick 30 yards from the Swans goal deflected off the wall and onto the bar. Chapple again getting forward shot inches wide across the goal before substitute Kwai Marsh-Browns shot was stopped by Adams in injury time.
Slimbridge now out of the FA Cup are left to concentrate on the league with two important games this weekend. The Swans travel to Frome Town on Saturday before returning home on Bank Holiday Monday afternoon welcoming local neighbours Cinderford Town to Thornhill Park.
For those not travelling to Frome on Saturday, the reserves entertain Tuffley Rovers development side in a Hellenic League Division 2 fixture at Thornhill Park with a 3pm kick off.
Slimbridge: L Adams, B Deakin, B Prictor, B McLean, N Dennis, T Lawrence, E Mbunga, B Hands, W Hawes, M Ford, M Thomas
Subs Used: J Flo, J Martin, I Thurston
Attendance: 208
Supporters player of the match: Lewis Adams