The Hares looked to be on course for an impressive Thurlow Nunn League First Division North success when easing into a two-goal lead at high-flying Mulbarton Wanderers.
But a controversial dismissal in the aftermath of their second goal proved to be a key moment with the hosts then powering to a 4-2 success.
Defender Scott Callaghan wrongly picked up a second caution for delaying the re-start of the match for an offence actually committed by Hares team-mate Toby Allen.
"It is probably the most annoyed I've ever been after a game," said Hares chief Brett Whaley.
"I'm not a referee-basher by any means but one very poor decision completely changed a really important game for us.
"We played very well for an hour against another set of promotion hopefuls, but the momentum swung drastically in that moment.
"Wee also have to look at why we conceded so many goals in such a short space of time after the red card regardless of how aggrieved we were about the decision itself.
"But the end result is three points that we know should be ours have gone to another of our rivals to go up.
"That is a huge kick in the teeth, but we play Mulbarton again before Christmas at our place and we have the opportunity to take those points back."
Leading scorer Jack Friend put March ahead with the only goal of the first half and the hot-shot then doubled their advantage on the hour.
But the dismissal of Callaghan before the match resumed proved to be pivotal as Mulbarton immediately made the most of their numerical advantage to strike four times.
That unfortunate sending off could also prove to be Callaghan's final involvement in the Hares' season.
He went under the knife earlier this weekend for surgery on a knee ligament problem and now faces a lengthy recovery.
March, who fell to seventh place and are three points off the top four, will attempt to bounce back to winning ways in the First Division North when they go to struggling Felixstowe & Walton United Reserves tomorrow, 3pm.
Hares chief Whaley has added former Wisbech Town attacking ace Dylan Edge to his squad. Edge arrives from another of Whaley's former clubs, Step 4 side Yaxley.
But wideman Flo Tsagium has left March to join fellow Thurlow Nunn League First Division North side Wisbech St Mary.