Didcot Town blew the chance to boost their BGB Southern League Division 1 South & West play-off bid as they crashed to a shock 2-1 defeat at Cirencester.
The result means they are just three points ahead of nearest challengers Thatcham in a play-off place.
Didcot started brightly with Elliott Osbourne-Ricketts fizzing a shot wide, before Josh Dutton-Black and Sampson saw efforts well blocked by Cirencester keeper Tom King.
Cirencester took the lead when Carl Brown beat keeper Michael Watkins with a cool finish after Didcot failed to deal with a long clearance.
Seconds later, Sampson got in a crucial block on Andrew Minturn’s header.
After the break, Neville Roach and James Mortimer-Jones combined to put Dutton-Black clear, but his shot was smothered.
A move involving Paul Powell, Roach and Jack King culminated in the ball being laid back to Sampson, whose shot hit the inside of a post.
Just as it looked as though Didcot would level, they went 2-0 down, Jason Welsh heading into the top corner following a corner from Steve Davies.
Sampson reduced the deficit when his shot was deflected in.
Late on, Dutton-Black had two half-chances to rescue a point, but King was equal to the first effort and the second went over.
Didcot Tn: Watkins, Heapy, Powell, Williams, Brown (Hopkins 76), Mortimer-Jones, Sampson, King, Osbourne-Ricketts, Roach, Dutton-Black.
Attendance: 173.
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