A depleted Cheltenham were unable to kick-start their season on the banks of the Thames as Marlow edged a tight game.
The hosts started brightly and after a fine move down the right took the lead in just the third minute with a try from danger man centre George Jafari.
Joylon Kelleher converted to give the hosts an early seven-point advantage.
Cheltenham did their best to find an immediate response and soon found themselves two men to the good with Mark Gindrod shown a yellow card for killing the ball and Sam Butler joining him in the sin bin for dissent.
But try as they might Cheltenham were unable to unlock the Marlow defence as the hosts survived a sustained onslaught from the visitors.
Indeed, they extended their lead with a sweetly-struck Kelleher penalty after Ben Constantine became the first Cheltenham player to see yellow after being found guilty of obstruction.
Worse was to follow for Cheltenham as Marlow ran the ball at speed to open up the defence and allow Kelleher in for a try he duly converted.
That made the half-time score 17-0 to the hosts and Cheltenham missed a golden chance to cut the deficit in the opening minutes of the second period, but Rob Whitehouse sliced a penalty wide from in front of the posts.
Whitehouse further blotted his copybook with a yellow card before Oli Young finally opened the visitors’ account for a fine try coverted by Ryan Hill.
Marlow then lost Jack Rider, son of former BBC TV sport Presenter Steve Rider to injury, while Cheltenham’s Mark Whitney was sidelined with a knock to his leg.
Cheltenham were first to settle after the restart and after good play from the pack Constantine grabbed a try converted by Hill to set up a grandstand finish at 17-14. But Marlow had other ideas and wing Matt Saunders found the defence wanting to skip over for an uncoverted try. From the restart Marlow gained turn over ball and Pete Lewis trotted over for a try converted by Kelleher to seal the Marlow victory. Cheltenham did, however, have the last word with Whitehouse scoring a try converted by Hill with the last play of the match.
MARLOW: Westnall, Butler, Cook, Martin, James, Bailey, Grindrod, Rodgers, Rider, Kelleher, Noble, Lewis, Jafari, Saunders, Pincott. Replacements, Smyth, Stewart, Watt.
CHELTENHAM: Moore, Griffiths, Seymour, Milne, Dustin, Constantine, Jackson, Lait, Young, Hill, Haskayne, Whitney, Whitehouse, Morris, Ratcliffe. Replacements, Clifford,Cox.
REFEREE: Scott Galbraith Oxfordshire RFU
STAR MAN: Mark Whitney