The Ducks took the lead in the 18th minute when Steve Grenfell?s corner was eventually only half cleared and the ball ran free to Cliff Hercules who buried his shot past Marlow keeper Gary Lester for his 12th goal of the season.
It was 2-0 in the 44th minute when, from another Grenfell corner, Lester missed the ball under pressure from Hercules and Graham Westley stooped to head home at the far post for his 5th goal since joining the club.
Then, in stoppage time at the end of a first half dominated by United, it was 3-0 when Grenfell?s inswinging free kick from the left edge of the box found Hercules who headed past Lester to leave the hosts with a mountain to climb.
Marlow pulled a goal back in the 51st minute when future Duck John Caesar and Ansil Bushay combined with Caesar?s shot being blocked by United keeper Bill Davies before Bushay converted the rebound for his 16th goal of the season.
Just four minutes later they pulled another one back when a great through ball by David Lay released Mark Watkins who brilliantly chipped Davies for his 13th of the season.
The goal flurry continued and in the 58th minute it was 4-2 United when a through ball by Andy Robinson found Westley who fired past Lester, although the keeper perhaps should have saved the shot.
The hosts made a number of good openings which saw Lay hit a post and Bushay have one effort cleared off the line by Robinson before the pressure saw them pull another goal back in the 81st minute when United new boy Phil Stacey was adjudged to have brought down Watkins in the box and Lay scored from the resulting penalty.
However, Dave Sansom?s side held out to move up to 7th in the table and leave Marlow in 4th from bottom.
David Figg