Two goals from skipper Dave Allen - who was also the scourge of Burnham last month-condemned the Rebels to their third defeat in a row.
This loss, coupled with Bracknell's 1-1 draw with fellow-strugglers Andover, leaves Slough just two points clear of the drop zone.
With just 11 games left, the Rebels' Southern League status is starting to look more than a bit precarious. Rock-bottom Newport IOW are all but relegated already going into the final quarter of the season. This leaves Slough, Bracknell and Andover, separated by just three points, vying to avoid finishing second bottom.
Looking at the remaining fixtures all three relegation-threatened sides have tricky run-ins. One thing that weighs in Slough's favour, however, is the fact that they still have to play Newport, which will be an ideal opportunity to pick up all three points.
Tuesday's encounter between Bracknell and Andover will be viewed as a must-win by both sides, while the Easter Weekend, which sees Slough play local rivals Burnham and Windsor in the space of two days could well hold the key for the Rebels.
Winchester City Line up
Davies, Wilson, Lang, Parfitt, Gilliam, Llewellyn, Knight, Allen (c), Hussey, Taplin, Lockyer. Substitutes: Bowler, Gregory, George, Jacob, Gray.