Gavin Hoyte's first career goal gave 10-man Barnet a 1-0 win over in-form Bristol Rovers.
The full-back volleyed home from close range in the fifth minute for the Bees, who later had captain Andy Yiadom sent off, to inflict a first defeat in eight on the promotion-chasing Pirates.
Rovers striker Ellis Harrison twice went close to equalising before the break, heading straight at Bees goalkeeper Jamie Stephens when unmarked before nodding Daniel Leadbitter's cross narrowly wide.
Harrison, without a goal since October, forced another save from Stephens minutes after the restart before midfielder Yiadom was shown a straight red card for a lunging challenge on Stuart Sinclair.
The visitors, beaten to the Conference title by their hosts last season and cheered on by more than 1,200 travelling fans, dominated possession following the dismissal but struggled to create clear chances.
Substitute Liam Lawrence lashed narrowly over from the edge of the box on his Rovers debut, while midfielder Sinclair also saw an effort from range go too high.