Well made a bright start and could've been two up early on with Derek Stillie saving one on one with David Clarkson, before Scott McDonald's shot was blocked.
Well were made to suffer for not taking their early chances when on 28 minutes the visitors took the lead, Craig Conway skipped past Paul Quinn and sat up a cross for Collin Samuel to volley home at the far post.
United were dealt a blow two minutes later when Christian Kalvenes committed his second stupid tackle of the afternoon and was shown a second yellow and therefore a red.
Despite this setback the visitors were two up by half-time when David McCracken got on the end of Lee Mair's flick from a Conway corner.
Just after the hour mark Motherwell were thrown a life line when Alan Archibald needlessly fouled Darren Smith in the box. Richie Foran took the kick and despite Stillie going the right way he scored his fifth goal in four games.
It was game on now and after being denied what looked like another stonewall penalty, Well equalised when Mark Reynolds rose to head a Jamie Paterson corner past Stillie on 67 minutes.
United were back in front with 12 minutes left when Barry Robson found space from a throw-in and played in a cross for the unmarked Noel Hunt to head past Colin Meldrum inside the six-yard box.
McDonald could've grabbed another equaliser with five minutes from the end as he burst down the left, but he shot at Stillie at his front post with support waiting in the middle.