Coyne's goal added to a first-half poacher's effort from Dan Burnell, and Adam Logie grabbed another late on as Slough maintained their strong start to the season.
Fresh from a 3-0 win over Fleet on Saturday, Slough looked in confident mood early on, looking for another win at Oak Tree Road, having won 4-1 here last season with Dan Burnell bagging a hat-trick.
Whilst the early play was fairly even and concentrated in midfield, Slough had the first shooting chance as Dom Marsala, restored to the starting eleven in place of Stuart Swift, battled his way into the box past Jon Case, but his fierce strike was easily held at the near post by Charlie Fanner, who has joined Marlow from Slough the previous week.
Sean Fraser wasted a good shooting opportunity for the hosts but otherwise threatened little, and Slough started to apply the pressure, with Adam Logie volleying over from six yards as Sonner nodded down from a corner.
Minutes later, John Gray superbly cleared off the line after Danny Murphy’s superb cross was attacked by Sonner, who won it ahead of Fanner.
But the pressure told with 28 minutes played, with a sense of inevitability about the scorer. Burnell held the ball up well in midfield and laid it off to Sinclair. Paul Coyne burst away on the overlap, and his teasing low cross was fumbled by Fanner – with poacher Burnell on hand to punish Marlow and tuck away his fifth goal of the season.
Slough could have scored a second soon after, but Logie's header somehow came off Burnell and into Fanner's grateful arms.
Marlow seemed to lack attacking flair and threatened only from distance, with James Warrington dealing with a John Gray free kick very comfortably.
The pattern was to remain the same in the second half – Marsala went close after confusion between Fanner and Mark Avery, but Warrington had to be alert to keep out a Nathan Jack header in a rare lapse in concentration from the Slough back four.
Burnell and Sonner went close again as Slough threatened to score with every attack, with Fanner looking less than confident against his former club. On the other hand, Warrington, although rarely tested, grew into the game and looked confident in the air.
Slough survived a spell of Marlow pressure, which saw the Blues win a series of corners but not threaten the goal, with Jack well blocked as he attempted a shot.
Whilst Slough always looked the more likely to add to the score, few would have predicted the source when it eventually came. Paul Coyne collected the loose ball after a defensive clearance, advanced just inside the Marlow half, and with a superb piece of vision and skill, spotted Fanner a sufficient distance off his line to attempt an audacious lob, which sailed over the goalkeeper and into the top corner to all but seal the points and double his personal Rebels goal tally.
Understandably dejected by this, Marlow almost pushed the self-destruct button as a short back pass was seized upon by Coyne, but Fanner kept out his effort.
Charlie Mpi and Ben Abbey were introduced as Slough looked to add to the score, and were cruising to victory by the time the third goal arrived. Minutes after Marsala’s free kick was tipped over by Fanner, Mpi went close but with a minute remaining, Sinclair crossed in from the right and Adam Logie powered in a header which Fanner could not keep out, the defender registering his second goal of the Bank Holiday weekend.
Despite the result, the match ended in some disappointment for Slough, as substitute George Coyle was forced off after suffering a blow to the face – which was later revealed to be a fractured cheekbone, a repeat of an injury he suffered playing for Chesham United’s reserves in 2006.
Marlow Line up
Charlie Fanner, Jon Case, John Gray, Tom Willment (c), Mark Avery, Dan Willment, Ashleigh James (John Mbamarah), Stuart Maclellan, Sean Fraser (Marcus Mealing), Gavin Lane (Jermaine Roche), Nathan Jack. Subs not used: Zac Gill, Daniel Stone.