A solitary goal was enough for Grays Athletic to beat a below-par Dereham Town in a crucial game at Aldiss Park.
Lewis Clark headed in from a first-half corner to cement the visitors' place in the Isthmian League North's top five.
The 1-0 defeat means Dereham now face an uphill struggle to make the play-offs themselves.
Adam Gusterson's men now sit in seventh place on 60 points - five behind Grays with just three matches remaining.
The Magpies manager was particularly disappointed given the Essex outfit were reduced to 10 men just before half-time.
"It’s a disappointing defeat and a wasted opportunity for us," he said.
"We didn’t do enough with the man advantage to get back in the game, and it’s another very soft goal to concede that has cost us."
Dereham, without the injured Rhys Logan, made a promising start on Saturday when Luke Johnson was put through on goal after four minutes but skewed wide from close range.
Grays responded, however, through Freddy Moncur who fired wide, before skipper Clark put his side in front on 16 minutes.
During an even first half, Grays keeper Danny Sambridge got down low to save a left-footed drive from Shaun Bammant, while Moncur again failed to hit the target.
The away side's red card came after 40 minutes, when Callum Leahy dismissed following an altercation involving Bammant.
Hoping to build on the man advantage, Gusterson sent on Cambridge United loanee Dan Barton at the break.
But Dereham struggled to find creativity and rhythm in their play, regularly overhitting passes with a strong wind now behind them.
Magpies captain David Hinton put Bammant through on goal just after the hour mark, but Sambridge did well to smother the ball at the attacker's feet.
Bammant and Moncur exchanged efforts on goal, before a superb last-ditch tackle from Dion Frary prevented Ryan Melaugh from increasing Grays' lead with a quarter of an hour remaining.
Try as they might, the hosts could not find a way through a solid Grays defence.
Sambridge beat Bammant to the ball after Matt Castellan pumped a long pass forward, before making a good save to deny Hinton.
In added time, Rossi Jarvis saw a close-range effort deflected narrowly wide.
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