Winchester are sliding dangerously into South Premier Division relegation waters after a run of eight matches without a win, the last three of which they have lost.
Now third from bottom of the log, they are now only four points ahead of Henley, who have closed the gap by winning two of their last three games.
Horsham lie bottom of the table and are expected to finish last.
Winchester have four games left, with the visit to Henley on Saturday week likely to be critical towards their immediate future.
Although actual relegation places are largely dependent on demotions from the National League feeder Conferences, Winchester will want to avoid finishing in second from bottom spot.
They failed to take advantage of a fast start against Spencer, who scored three times in a blistering ten minute second half spell to run out eventual 4-3 winners at Kings’.
Despite taking an early lead through Jack Culmer and dominating the first period with plenty of possession Winchester were unable to carve out many clear cut chances.
Gradually Spencer picked up the tempo and equalised through Gus Kennedy just before the break.
Both sides probed for opportunities which were far and few between before the game burst into life in the last 15 minutes.
A Winchester penalty corner was blocked by a defender’s foot and Ben Hibberd converted the resulting stroke to give his side a 2-1 lead.
Spencer responded promptly with three goals in 10 minutes through Stewart Laing, Ashley Smith, Tom Whiteley to forge 4-2 ahead.
Winchester noticeably flagged, but indiscipline by Spencer led to the visitors being reduced to nine men and Craig Jeffrey clawing back a third goal for Winchester, which proved too late to change the outcome.
* Trojans went down 3-2 at Guildford, where Richard Aves and Colin French were on target.
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