Lynn's play-off push suffered a huge blow as they crashed to a damaging defeat against 10-man Dorchester.

The Linnets, five points outside of the Southern League Premier Division top five, going into the game had hoped to maintain their momentum. But they were hit by a late sucker punch as they failed to extend their unbeaten run to six matches.

Nathan Walker's opener on the stroke of half time had put the visiting Magpies in front although their cause wasn't helped when Franklyn Clarke was dismissed for a second bookable offence in first-half injury time.

Lynn eventually equalised through Jacek Zielonka with about 20 minutes to go and looked set to pick up, at the very least, a point. Yet their hopes of staying in touch with the top five were rocked when Walker doubled his tally at the death – minutes after the home side's Liam Hurst had missed a sitter to win it – to stun the Linnets.

Lynn went into the match having not played for a fortnight after last Saturday's home postponement against Hungerford Town. However, Matty Castellan and Zielonka did get 90 minutes under their belt in midweek for the club's reserve team in the Norfolk Senior Cup – as did substitutes Toby Hilliard, Dylan Edge and Sam Mulready.

Gary Setchell was forced into making a rare defensive change with Ryan Fryatt being ruled out with an apparent illness. His place was taken at right-back by usual captain Sam Gaughran.

Fryatt's replacement was involved in the game's first key moment with less than two minutes on the clock. He picked out David Bridges after Henry Lander had missed his clearance but Dorchester keeper Shane Murphy raced off the line to save with his leg.

Lynn's bright start faded somewhat with Lee Stevenson causing frustration by failing to pull the trigger twice when well placed. Hurst then dragged wide after some great play near the corner flag involving Lee Smith and Gaughran.

Stevenson almost broke the deadlock in the 37th minute but his hooked effort over Murphy was hacked off his own line by the covering Nick Crittenden. Murphy dived at Bridges' feet to deny the hosts moments later as they tried to end the half on a high.

Neil Martin fired a warning sign when he headed wide with five minutes to go and it wasn't long before the Magpies were celebrating. The unchallenged Martin's centre from the left was headed goalwards by Walker. Alex Street saved with his legs and protests that the ball had crossed the line were ended instantly when the Magpies' number nine prodded home at the second attempt.

It was a massive blow for the Linnets who had been the better side. But they received a huge boost in injury time when Clarke picked up his second yellow and was sent for an early bath after failing to keep his mouth shut. Lynn's Michael Clunan was also cautioned for his part in the spat to pick up a two-game ban for his 10th booking of the campaign.

Stevenson lifted over from 10 yards early after the restart as the hosts pushed for an equaliser. Setchell strengthened their search by replacing defender Kern Miller with frontman Mulready.

As the Linnets pressed forward, left-back Jordan Yong found himself in an advanced position. His deep, deep cross found Stevenson but his header at the far post was tipped over by Murphy. The same man worked Dorchester's keeper a few minutes later but this time his save was even more comfortable.

Murphy stood absolutely no chance with Zielonka's drilled shot that brought the two teams level. The Pole's effort arrowed into the bottom corner to raise the roof – and hopes of a crucial comeback being completed.

As the visitors fell deeper and deeper, Lynn kept pressing. Another fine Yong foray resulted in Stevenson's weak effort being saved.

Hurst had the hugest chance to wrap up what would have been a priceless win when he was picked out by Mulready. But he incredibly blazed over from inside the six-yard box.

And he was made to pay for it in the most heartbreaking style as Walker ghosted in at the back post to latch onto a long ball and roll home.

Lynn (4-1-4-1): Street, Gaughran, Miller (Mulready, 58), Castellan, Yong, Clunan (Hilliard, 82), Hurst, Smith, Bridges, Zielonka, Stevenson (Edge, 90+2). Subs not used: Friend, Pearson. Booked: Clunan. Goal: Zielonka (71)

Dorchester (4-1-4-1): Murphy, Crittenden, Smeeton, Jermyn, Lander, Dillon, Clarke, Bowles, Walker, L Holmes (T Holmes, 67), Martin. Subs not used: Tarbuck, Brookes, Proffitt, Walker-Harris. Booked: Bowles. Sent off. Clarke (2 yellows), T Holmes. Goals: Walker (44, 88)

Referee: O Morris-Sanders

Attendance: 523