Morgaro Gomis struck twice after David Goodwillie scored his ninth goal of the season from the penalty spot.

The victory gives United 45 points from 27 games, good enough for third after Hibernian were held to a 1-1 draw at home to St Johnstone.

Liam Craig dispatched a late penalty at Easter Road to frustrate the Saints, who had led from a third-minute spot-kick of their own, fired in by Anthony Stokes.

Craig's 85th-minute effort came after Derek Riordan had a shot cleared off the line as Hibs looked to double their lead.

Hibs are one point behind United and three above Motherwell, who beat Kilmarnock 1-0 at home.

Jamie Murphy got the only goal, his deft header in the 69th minute giving Motherwell a massive 12-point cushion over seventh-placed Aberdeen, whose miserable run continued with a lunchtime defeat to 10-man Hearts.

It is now eight matches since the Dons last tasted victory.

Today they went down 1-0 but it was a worthy winner with Eggert Jonsson firing in a stunning overhead kick in the 64th minute.

That came 12 minutes after Hearts substitute Laryea Kingston was shown a straight red card for a high challenge on Fraser Fyvie.

Today's other match between St Mirren and Hamilton ended in a goalless draw.