An hour of excellence was undone by 30 minutes of mediocrity as Kingstonian fell to a 2-1 home defeat to play-off rivals Canvey Island on Saturday.
Their ninth defeat of the league campaign means they drop to seventh.
With Wealdstone, Concord Rangers and Lowestoft looking odds-on to take three of the four play-off spots, the fight is now on for the final place.
Manager Alan Dowson admitted that the next few weeks will prove crucial to hopes of promotion.
“It’s a must win now,” he said of Tuesday’s match at Harrow.
“We’ve got games in hand on Canvey and we’ve got to win them. If we play like we did in the first 60 minutes today, we’ll be fine.”
Indeed this was a game Kingstonian dominated and never looked like drawing, let alone losing, after Andre McCollin opened the scoring in 24th minute.
Lewis Taylor, so often the driving force of the K’s midfield in recent weeks, made a characteristic burst through the centre and sent a perfectly weighted pass into McCollin’s path. The striker opened up his body to knock the ball left-footed past the advancing Ashlee Jones.
It was his 15th goal of a fine season. McCollin had already had a superb effort saved on to the crossbar while Paul Vines missed a sitter from two yards out as K’s attacked with verve and purpose on a bitterly cold afternoon.
The pattern continued after the break, with Vines denied by another brilliant Jones save while the returning Ian Gayle looked to be keeping a lid on Canvey's occasional forays forward.
Then, out of nowhere, the game turned. Tom Bird and Kieran Murphy collided under a high ball to let Kevin Dobinson through, who squared to a grateful James Rowe to score.
And with 10 minutes remaining, Ryman League chaos theory struck again, when Bradley Woods-Garness finished from 6 yards out to give the Gulls all three points.
“There’s not much wrong. Performances have been good,” said Dowson.
“We were outstanding at the back, doing everything right, and then suddenly it’s two defensive mistakes… by my left-back and centre-back which were laughable really.
“Then Canvey upped their game because our lads thought ‘we can’t believe this, we’ve been on top for so long’.”
After the trip to Earslmead tomorrow night (Tuesday), K’s host East Thurrock United at home on Saturday.