Rory MacLeod opened the scoring for the visitors after eight minutes but a Connor Young penalty shortly before the interval squared the game. United had a man sent off midway through the second period and Malik Zaid grabbed what turned out to be the winner.
United coach Ryan Moon was sent off at the death as Hibs held on for a vital three points in their bid for league glory.
There hadn’t been much between the two teams when United took the lead. Keir Bertie picked out Miller Thomson on the right flank and the latter played in MacLeod, who swivelled before finishing past Murray Johnson from 20 yards out.
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Young then had a couple of chances at the other end, shooting wide before Zaid’s deflected effort from Ethan Laidlaw’s pass fell to Young whose effort was somehow saved by the foot of Ruairidh Adams who had dived the other way.
Hibs kept pressing for an equaliser and five minutes before half-time referee Konrad Spalony pointed to the spot, adjudging Thomson to have fouled Oscar MacIntyre.
Young dispatched the penalty past Adams to restore parity and take his recent tally to seven goals in four matches.
Defender Mack Weir had the ball in the net shortly after the restart but it was ruled out for offside.
The second half was attritional, Hibs pushing for another and United coping well until shortly after the hour mark when the visitors were reduced to ten men. Jacob MacIntyre rushed to the away dugout to collect the ball for a throw-in, with a member of the United coaching staff punching the ball away.
Sam Lovie, who had been cautioned in the first half, was shown a second yellow card and dismissed for time-wasting.
Moments later came the decisive moment in the match; Lewis O’Donnell’s pass out from the back was intercepted by Young who split open the defence with a perfectly-weighted through-ball for Zaid, who lifted the ball over the onrushing Adams for what turned out to be the winner.
Young fired wide late on and Josh McCulloch blazed over as Hibs saw out the game for three vital points.